Monday, May 23, 2016

Should We Test for Cointegration Using the Johansen Procedure If We Want to Estimate a Single Equation Static Regression?

A student from Cuba asked me:

"I want to apply the DOLS methodology... I have read several books and research works about DOLS but none of them explain clearly how to test cointegration in this case.... I asked some professors about this issue and one of them told me that I should apply the Johansen cointegration test."

It's quite easy to find papers that do this - first test for cointegration using the Johansen procedure, report only the cointegration test statistics, and if they can be used to reject the null hypothesis of non-cointegration then use some other method such as Dynamic Ordinary Least Squares (DOLS) to estimate a static single equation regression model. These researchers aren't actually interested in the complete vector autoregression (VAR) system, which is OK. I've reviewed quite a lot of papers that use this approach.

If your model has more than two variables (one dependent variable and one explanatory variable) then this is a very bad idea. The cointegration test statistics from the Johansen procedure (if they reject the null) say nothing about the cointegration properties of your single equation regression model.

The following simple example shows why. Imagine we have three variables, X1, X2, and X3 with the following "data generation process":


where epsilon 1 is a stationary stochastic process and epsilon 2 and 3 are simply white noise. Variables X2 and X3 follow simple random walks. Variable X1 cointegrates with X2. But X3 is a random walk that has nothing to do with the other two variables. If you estimate a VAR with these variables and do the Johansen cointegration test, you should expect to find that there is one cointegrating vector. But the following regression:


will not cointegrate. It is a spurious regression because it includes X3 which is an unrelated random walk. We cannot rely on finding that the VAR "cointegrates" to assume that this regression also cointegrates. Only X1 and X2 cointegrate in this example. Of course, it is possible that X1, X2, and X3 are jointly cointegrated but as this example shows, that doesn't have to be the case.

How can we avoid this? The cointegrating vector in this case is [1, -beta1]. We could test within the Johansen procedure whether we can restrict the cointegrating vector to not include a coefficient for X3. Unlike gamma3 in the static regression, if X3 does not belong in the cointegrating relationship, then this coefficient is expected to be zero. We can and should also test the residuals of the static regression to see if they cointegrate.

Tuesday, May 17, 2016

Stochastic Trend Included in Top 100 Economics Blogs!

Economics Blogs

I'm honored that Stochastic Trend has made it into a list of the top 100 economics blogs, albeit at position 99. It's a good list of possible blogs to follow.

Friday, May 13, 2016

"Replicating" the Climate Contest

My previous post discussed Doug Keenan's climate contest. I wondered how accurate we could actually expect to be in such a situation. I assume that the temperature series is a simple random walk, possibly with a constant drift term. We want to see how accurately we can determine whether there is a drift term in the random walk or not.

So, again just using Excel, I created 1000 series of 134 observations each distributed as Normal(mu, 0.11), where mu is the drift term. For 250 series I set mu to 0.01, for 250 series I set it to -0.01 and for 500 to 0. I then compute the usual t-test for the significance of the sample mean for each series.

Only 127 t-tests were significant at the 5% level and 201 at the 10% level. Using a 10% significance level, statistical power - correct rejection of the incorrect null hypothesis of no drift - is 29%. Using a 5% significance level, power is 20%. There is no distortion of the actual "size" of the test - the number of incorrect rejections of the true null.

So, combining this information, if you use this method and a 10% significance level you will get 595 correct classifications of whether a random walk has a drift or does not have a drift, which is far below the 900 required to win the contest.

Of course, it seems that Keenan's data is a bit more complicated than this and may or may not have any relevance to the actual nature of climate data or the nature of the climate change problem.

You can download my data here. The first column is the drift term used and the first row indicates the years and the statistics columns.

More Mathiness in Climate Econometrics: Doug Keenan's Climate Change Contest

My colleague Robert Kaufmann got an e-mail from Doug Keenan inviting him to participate in his "climate change contest" without the usual $10 submission fee. I hadn't heard about this contest and went to the site to investigate. So, Keenan has produced 1000 time series of 135 observations each that are somehow derived from random numbers and then added a plus 1 or minus 1 per 100 observations trend to some of these. The series have been calibrated so that the they could potentially reproduce in some way the observed global temperature time series from 1880 to the present without an added trend. The task of the contestant is to determine for each series whether it has an added trend or not. If any submission gets 90% of these or more right by 30th November, this year, that submission will win $100,000.

Keenan's idea is that no-one can validly detect with 90% accuracy whether there is a trend in temperature or not. Therefore, the IPCC's claim that temperature has definitely increased over the last century and it is very likely that this is due to human activity must be wrong.

I downloaded the data. Looking at some of the series it's pretty clear that they are some sort of random walk (stochastic trend). It is not simply a series of random numbers (white noise) with a linear trend added. I haven't bothered to write a program to test this. Assuming that they are simple random walks, I tested in Excel whether the mean of first difference was different to zero for each of the thousand series. Only 8 of the series have a mean first difference that is significantly different to zero at the 5% level using the standard calculation of the standard error of the mean, which assumes that the first differences are white noise. If they were normally distributed white noise and none of the original series had an added trend then we would expect about 50 of the means of the first differences to be significantly different to zero by the definition of statistical significance. So, something else seems to be going on here. I expect that statistical power to detect a non-zero drift term of 0.01 or -0.01 when the standard deviation of the first differences is 0.11 is in any case rather low. Perhaps we could use structural time series methods, but statistical power of 90% at a significance level of 10% is a lot to ask for in this situation. I created my own dataset to see how many series one could expect to correctly classify - statistical power using a simple data generating process and a simple test was 29% for a 10% significance level test. This means that we can only correctly classify 595 of the 1000 series.

The real question to ask is whether Keenan's thought experiment makes sense. I would argue that it doesn't. His argument is that if temperature follows some kind of integrated process then it is very hard to determine whether it has a drift component or will sooner or later just stochastically trend down again. Therefore, we can't know if temperature has statistically significantly increased or not. But theory and climate models predict that global temperature should be stationary if radiative forcing is constant. If we detect a random walk or a close to random walk signal in the temperature data then something else is happening. Research can then try to determine if it is likely to be due to anthropogenic factors or not. It is possible that we make a type 1 error - falsely rejecting the null hypothesis - but we can determine how likely that is. So, in my opinion, Keenan's contest is another case of mathiness in climate econometrics.

Saturday, April 16, 2016

The Time Effect in the Growth Rates Approach

After a very long process our original paper on the growth rates approach was rejected by JEEM about a month ago. I think the referees struggled to see what it added to more conventional approaches. A new referee in the 2nd round hadn't even read the important Vollebergh et al. paper, so it's not surprising they missed how we were trying to build on that paper. That, discussion with my coauthor, Paul Burke, and preparing a guest lecture for CRWF8000 on the environmental Kuznets curve, got me thinking about a clearer way to present what we are trying to do. It really is true that teaching can improve your research!

Vollebergh et al. divide the total variation in emissions in environmental Kuznets curve models into time and income effects:

where G is GDP per capita, E is emissions per capita, and i indexes countries and t time. They point out that the standard fixed effects panel estimation of the EKC imposes very strong restrictions on the first term:
Each country has a constant "country effect" that doesn't vary over time while all countries share a common "time effect" that varies over time. They think that the latter is unreasonable. Their solution is to find pairs of similar countries and assume that just those two countries each share a common time effect.

In my paper on "Between estimates of the emissions-income elasticity" I solved this problem by allowing the time effect to take any arbitrary path in any country by simply not modeling the time effect at all and extracting it as a residual. The downside of the between estimator is that it is more vulnerable to omitted variables bias than other estimators.

We introduced the growth rates approach to deal with several issues in EKC models, one of them is this time effects problem. The growth rates approach partitions the variation in the growth rate of emissions like this:

where "hats" indicate proportional growth rates, and X is a vector of exogenous variables including the constant. The time effect is the expected emissions growth rate in each country when the economic growth is zero. This is a clear definition. The formulation allows us to model the time effect in each individual country i as a function of a set of country characteristics including the country's emissions intensity, legal origin, level of income, fossil fuel endowment etc. I don't think this is that clear in the papers I've written so far. We focused more on testing alternative emissions growth models and, in particular, comparing the EKC to the Green Solow and other convergence models.

So what do these time effects look like? Here are the time effects for the most general model for the CDIAC CO2 data plotted against GDP per capita in 1971:


Yes, I also computed standard errors for these, but it's a lot of hassle to do a chart with confidence intervals and a continuous variable on the X-axis in Excel.... There is a slight tendency for the time effect to decline with increased income but there is a big variation across countries at the same income level. And here are the results for SO2:

These are fairly similar, but more negative as would be expected. Clearly the time effects story is not a simple one and one that has largely been ignored in the EKC literature.

Thursday, April 7, 2016

Should We Stop Investing in Carbon-Free Energy So That We Will Be Able to Afford CCS?

Myles Allen has a new interesting paper in Nature Climate Change:"Drivers of Peak Warming in a Consumption-Maximizing World", which has attracted media attention. The article in The Australian is framed as: "If we spend money now on renewable energy we won't be able to afford carbon sequestration later". This didn't sound right to me as I'm an "all of the above" kind of guy when it comes to climate policy and if there is less carbon in the air that needs scrubbing in the future the less it would seem to cost to scrub it.

I haven't done a thorough read of the mathematics in Allen's paper and this isn't going to a proper critique of his article. I just wanted to understand where the journalist got this idea from.

Allen uses a very simple cost-benefit framework where there is "backstop technology" - a technology that can remove carbon dioxide from the atmosphere at constant cost. The key assumption I think is that the "social cost of carbon" depends linearly on the level of income per capita. The following graph illustrates the main result:
If economic growth is rapid, then the social cost of carbon will rise much faster than if economic growth is slow. Therefore, it will pay off earlier to employ the backstop technology. This means that, paradoxically, peak warming will be less than under slower economic growth.

It is a long leap from this to arguing that we shouldn't be investing in renewable energy. Allen's model allows for an efficient level of abatement until the marginal cost of abatement hits the backstop cost. Also the model has no feedback from abatement cost to the rate of economic growth, which is exogenous. Almost all economic research, including my own, finds that the growth costs of climate mitigation are very small, at least until extreme levels of abatement are reached. So, the model is an interesting thought exercise about CCS but doesn't have as strong policy implications as the media suggests.

Friday, March 11, 2016

Economic Growth and Global Particulate Pollution Concentrations

I have just posted another working paper in the Trends and Drivers series, this time coauthored with recent Crawford masters student Jeremy van Dijk.

Particulate pollution, especially PM2.5, is thought to be the form of pollution with the most serious human health impacts. It is estimated that PM2.5 exposure causes 3.1 million deaths a year, globally, and any level above zero is deemed unsafe, i.e. there is no threshold above zero below which negative health effects do not occur. Black carbon is an important fraction of PM2.5 pollution that may contribute significantly to anthropogenic radiative forcing and, therefore, there may be significant co-benefits to reducing its concentration. In our paper, we use recently developed population-weighted estimates of national average concentrations of PM2.5 pollution that are available from the World Bank Development Indicators. These combine satellite and ground based observations.

Though the environmental Kuznets curve (EKC) was originally developed to model the ambient concentrations of pollutants, most subsequent applications focused on pollution emissions. Yet, previous research suggests that it is more likely that economic growth could eventually reduce the concentrations of local pollutants than emissions. We examine the role of income, convergence, and time related factors in explaining changes in PM2.5 pollution in a global panel of 158 countries between 1990 and 2010. We find that economic growth has positive but relatively small effects, time effects are also small but larger in wealthier and formerly centrally planned economies, and, for our main dataset, convergence effects are small and not statistically significant.

Crucially, when we control for other relevant variables, even for this particulate pollution concentration data there is no environmental Kuznets curve, if what we mean by that is that environmental impacts decline with increasing income once a given in sample level of income is passed - the turning point.

The following graph shows the relationship between the average growth rates over 20 years of particulate pollution concentrations and per capita GDP:

The two big circles are of course China and India where both GDP and particulate pollution grew strongly. We can see that there is a positive relationship between these two growth rates, especially when we focus on the larger countries. The main econometric estimate in the paper shows that a 1% increase in the rate of economic growth is associated with a 0.2% increase in the growth rate of particulate pollution. This is much weaker than the effects we found for emissions of carbon and sulfur dioxides. The estimated income turning point is $66k with a large standard error. On the other hand, when we estimate a model without the control variables, we obtain a turning point of only $3.3k with a standard error of only $1.2k. To check the robustness of this result, we estimate models with other data sets and time periods. These yield quite similar results.

We conclude that growth has smaller effects on the concentrations of particulate pollution than it does on emissions of carbon or sulfur. However, the EKC model does not appear to apply here either, casting further doubt on its general usefulness.


Thursday, March 3, 2016

My Submission to Stern Review of the REF

The Stern Review of the REF (Research Excellence Framework) is the latest British government review of research assessment in the UK, following on from the Metric Tide assessment. I have just made a submission to the enquiry. My main comment in response to the first question (1. What changes to existing processes could more efficiently or more accurately assess the outputs, impacts and contexts of research in order to allocate QR? Should the definition of impact be broadened or refined? Is there scope for more or different use of metrics in any areas?) follows:

"I think that there is substantial scope for using bibliometrics in the conduct of the REF. In Australia the Australian Research Council uses metrics to assess natural science disciplines and psychology. Research that I have conducted with my coauthor, Stephan Bruns, shows that this approach could be extended to economics and probably political science and perhaps other social sciences. We have written a working paper presenting our results that is currently under review by Scientometrics.

The paper shows that university rankings in economics based on long-run citation counts can be easily predicted using early citations. The rank correlation between universities' cumulative citations received over ten years for economics articles published in 2003 and 2004 and citations received in 2003 to 2004 alone is 0.91 in the UK and 0.82 in Australia. We compare these citation-based university rankings with the rankings of the 2008 Research Assessment Exercise in the UK and the 2010 Excellence in Research assessment in Australia. Rank correlations are quite strong but there are differences between rankings based on this type of peer review and rankings based on citation counts. However, if assessors are willing to consider citation analysis to assess some disciplines as is the case for the natural sciences and psychology in Australia there seems no reason to not include economics in this set.

Previously, I published a paper, published in PLoS One showing that the predictability of citations at the article level is similar in economics and political science. This supports the view that metrics based research assessment can cover both economics and political science in addition to the natural sciences and economics.

I believe the REF review should seriously consider these findings in producing recommendations for a lighter touch future REF."

I also made briefer responses to some of their other questions. In particular:

5. How might the REF be further refined or used by Government to incentivise constructive and creative behaviours such as promoting interdisciplinary research, collaboration between universities, and/or collaboration between universities and other public or private sector
bodies?


"A major issue with the REF and the ERA in Australia is the pigeon-holing of research into disciplines, which might not match well the nature of the research conducted. This clearly will discourage publication in interdisciplinary venues that may not be as respected by mainstream reviewers. The situation is less acute in Australia where a single output can be allocated across different assessment disciplines, but I still think that assessment by pure disciplinary panels discourages interdisciplinary work in Australia. So, I imagine this is exacerbated in the UK.

7. In your view how does the REF process influence the development of academic disciplines or impact upon other areas of scholarly activity relative to other factors? What changes would create or sustain positive influences in the future?

Johnston et al. (2014) show that the total number of economics students has increased in UK more rapidly than the total number of all students, but the number of departments offering economics degrees has declined, particularly in post-1992 universities. Also, the number of universities submitting to the REF under economics has declined sharply with only 3 post-1992 universities submitting in the latest round. This suggests that the REF has driven a concentration of economics research in the more elite universities in the UK.

Johnston, J., Reeves, A. and Talbot, S. (2014). ‘Has economics become an elite subject for elite UK universities?’ Oxford Review of Education, vol. 40(5), pp. 590-609.

Thursday, February 25, 2016

Economic Growth and Particulate Pollution Concentrations in China

A new working paper coauthored with Donglan Zha, who is visiting the Crawford School, which will be published in a special issue of Environmental Economics and Policy Studies. Our paper tries to explain recent changes in PM 2.5 and PM 10 particulate pollution in 50 Chinese cities using new measures of ambient air quality that the Chinese government has published only since the beginning of 2013. These data are not comparable to earlier official statistics and we believe are more reliable. We use our recently developed model that relates the rate of change of pollution to the growth of the economy and other factors as well as also estimating the traditional environmental Kuznets curve (EKC) model.

Though the environmental Kuznets curve (EKC) was originally developed to model the ambient concentrations of pollutants, most subsequent applications have focused on pollution emissions. Yet, it would seem more likely that economic growth could eventually reduce the concentrations of local pollutants than emissions. This is the first application of our new model to such concentration data.

The data show that there isn't much correlation between the growth rate of GDP between 2013 and 2014 and the growth rate of PM 2.5 pollution over the same period:



What is obvious is that pollution fell sharply from 2013 to 2014, as almost all the data points have negative pollution growth. We have to be really cautious in interpreting a two year sample. Subsequent events suggest that this trend did not continue in 2015.

In fact, the simple linear relationship between these variables is negative, though statistically insignificant. The traditional EKC model and its growth rate equivalent both have a U shape curve - the effect of growth is negative at lower income per capita levels and positive at high ones. But the (imprecisely estimated, so not statistically significant) turning point fro PM 2.5 is way out of sample at more than RMB 400k.* So, growth has a negative effect on pollution in the relevant range. When we add the initial levels of income per capita and pollution concentrations to the growth rates regression equation the turning point is in-sample and statistically significant. The initial level of pollution has a negative and highly statistically significant effect. So, there is "beta convergence" - cities with initially high pollution concentrations, reduced their level of pollution faster than cleaner cities did.

So what does all this mean? These results are very different than those we found for emissions of CO2, total GHGs, and sulfur dioxide. In all those cases, we found that growth had a positive and quite large effect on emissions. In some cases, the effect was close to 1:1. Of course, we should be cautious about interpreting this small Chinese data set. But our soon to be released research on global PM 2.5 concentrations, will again show that the effect of growth is smaller for these data than it is for the key pollution emissions data. This confirms early research that suggested that pollution concentrations turn down before emissions do, though it doesn't seem to support the traditional EKC interpretation of the data.

BTW, it is really important in this research to use the actual population of cities and not just the registered population (with hukou). If you divide the local GDP by the registered population you can get very inflated estimates of GDP per capita for cities like Shenzhen.

* The turning point is in-sample for PM 10.

Tuesday, February 23, 2016

Mathiness in Climate Change Econometrics

Terence Mills has a "white paper" on the Global Warming Policy Foundation Website. It predicts little future increase in temperature. Not surprisingly, The Australian has published a totally positive article about it. I commented in the comments there:

"Mills assumes that past fluctuations in temperature are purely random and of unknown causes and ignores greenhouse gases, or the sun, or volcanic eruptions, or any other specific factor that might drive climate change. He then fits simple statistical models based on this assumption to the data. Not surprisingly, if you assume that there isn't any specific factor driving the climate, your best forecast for the future is for not much change because you don't know what random shocks will show up to change the climate in the future. A more sensible approach is to test which of the various proposed drivers might actually have an effect and how large that effect has been. There are a lot of refereed academic papers that do just that including some I published myself. It's pretty easy to show that greenhouse gases have an effect on the climate, it's quite big (but fairly uncertain how big), and if emissions continue on a business as usual path there will be a lot of increase in temperature."

More technically: Mills fits univariate ARIMA models to HADCRUT,  RSS global lower troposphere series (only available since 1980) and Central England Temperature series. These include models with no deterministic component (an ARIMA(0,1,3) model of HADCRUT) and a model with a deterministic trend with breakpoints chosen based on "eyeballing" the temperature graph. None of these models predicts any future warming, because there is no trend in the trendless model and because the "hiatus" means there is no recent trend in the segmented trend model. Of course, a model with just a single linear deterministic trend fitted to HADCRUT data would forecast a lot of warming in the 21st Century, though with a very wide forecast error envelope. But that model isn't estimated, for some reason...

This is a prime case of "mathiness" I think - lots of math that will look sophisticated to many people used to build a model on silly assumptions with equally silly conclusions.

In other news, my paper coauthored with Luis Sanchez on drivers of greenhouse gas emissions is now published in Ecological Economics. It is open access till 12th April.

P.S. This post was cited in the Daily Mail.

Saturday, February 13, 2016

Family Portrait

This will slow things down for a while :) Noah was born two days ago. He is a very large baby - 4.71kg and 55cm long. If he was a t-statistic, he'd have 2 or 3 stars. He'll have to make do with one, his surname.*

* Stern = Star in German.

Saturday, January 23, 2016

PhD Applications Again

Three and a half years ago, I wrote a post about PhD applications. Since then, I have received a huge number of enquiries from prospective students. I now have two PhD students (Alrick Campbell and Panittra Ninpanit) and am on the committee/panel of two others (Anil Kavuri and Rohan Best). There are a couple of other good students who have applied but haven't come here because either their English test scores didn't meet our requirement or they couldn't get funding. We don't offer any new internal Crawford School scholarships at this point and I don't have any grant funds for PhD students. So, it is quite unlike applying for a PhD in the US where most students are funded by university sourced money in social sciences like economics. Here it is most likely that you will be funded by the Australian government one way or another, by your own government, or by an intergovernmental organization like the Asian Development Bank.*

As I mentioned in my previous post, also, unlike North America, applying to do a PhD in the social sciences and humanities here in Australia requires lining up a supervisor (=advisor) up front. Therefore, it is more like applying to do a PhD in the natural sciences and engineering in the US. Our formal process here also requires that potential students submit a research proposal, despite the fact that at ANU there is up to a year of coursework required in the economics program, which makes it seem more like a US PhD than most Australian PhD programs where you start doing research more or less straight away.

This is where I have been a bit frustrated by potential students submitting proposals that aren't at all related to the kind of research I do (despite this blog and my research webpage), proposals that are not very good, or being surprised that they need to submit a proposal because that isn't required to apply for a PhD in the US. Some of the latter seem like potentially good students. When I ask them for a proposal, the usual reaction is to write something rather quickly. I can't blame these students - when many programs around the world don't require a proposal, why should they invest a lot in writing one. One of the main reasons I did my PhD in the US rather than Britain was that I didn't know what to write a proposal about at the time. Another downside of a student submitting an upfront proposal is that they might then feel somewhat locked into that subject despite having written the proposal being a sunk cost. Alrick and Panittra were exceptions, having a pretty good proposal up front that was related to my research, which is why I agreed to supervise them.**

So, after receiving another off-the-wall topic from a prospective student this morning, I'm thinking of taking a radically new approach. Maybe, I should require students to submit a completed research paper (like we did when I was at RPI) instead of a  proposal for future research and then discuss this paper with the student to see how they think etc. I would require students to work on one of the broad areas I work on ("economic growth", "meta-analysis" etc.) and develop an actual proposal with them after they arrive here.

Or maybe the process is working exactly as it should? After all, I have had a few good applications and probably as many students as I should have. Any thoughts?

* Australian students can get an APA. Foreign students main option is the Australia Awards program. There are very few scholarships for students not from developing countries that Australia is interested in giving aid to. According to the government's Innovation Package, this will change dramatically.

** Students only need to line up the primary supervisor ahead of time. The other panel members usually join after the student has finished their coursework.

Friday, January 22, 2016

Follow-up on Anti-Vax

So, apparently my impression that anti-vax was a right wing cause (anti-government mandates/one-world government or whatever) was unusual and most people think it is a left-wing cause (anti big-pharma/pro natural remedies etc). Turns out that neither is the case and that there are people on both the left and the right (at least in the US) who are anti-vax. Actually, it seems that there is a slight maximum of concern about vaccines near the center of the political spectrum, as shown on this graph from the linked article:



Thursday, January 21, 2016

Drivers of Industrial and Non-Industrial Greenhouse Gas Emissions to be Published in Ecological Economics

My paper with my former master's student Luis Sanchez has been accepted by Ecological Economics. This is one of the papers in the series using growth rates estimators of the income-emissions relationship that came out of my work on the IPCC 5th Assessment Report. This is the second paper I have published based on work done in our course: IDEC8011 Master's Research Essay. The previous one was with Jack Gregory who is now a PhD student at University of California, Davis. BTW, we previously submitted this paper to Nature Climate Change, Global Environmental Change, and Climatic Change in that order, with the first submission on 5 January 2015.

Wednesday, January 20, 2016

Long-run Estimates of Interfuel and Interfactor Elasticities

A new working paper coauthored with Chunbo Ma on estimating long-run elasticities. This is one of the major parts of our ARC DP12 project, the "Present" part of the title: "Energy Transitions: Past, Present, and Future". We just resubmitted the paper to a journal and I thought that was a good time to post a working paper with the benefit of some referee comments.

Both my meta-analysis of interfuel elasticities of substitution and Koetse et al.'s meta-analysis of the capital-energy elasticities of substitution show that elasticity estimates are dependent on the type of data – time series, panel, or cross-section – and the estimators used. Estimates that use time series data tend to be smallest in absolute value and those using cross-section data tend to be largest.

We review the econometric research that discusses how best to get long-run elasticity estimates from panel data. One suggestion is to use the between estimator, which is equivalent to an OLS regression on the average values over time for each country, firm etc. in the panel. Alternatively, Chirinko et al. (2011) argued in favor of estimating long-run elasticities of substitution using a long-run difference estimator, which is very similar to the "growth rates estimator" we have used recently.

We apply both these estimators to a Chinese dataset we have put together from both public and non-public data sources. We have data for 30 Chinese provinces over 11 years from 2000 to 2010. We estimate models for choice of fuels - interfuel substitution - and for the choice between capital, labor, and energy - interfactor substitution.

A big issue with the between estimator, which has made it relatively unpopular, is that it is particularly vulnerable to omitted variables bias. The big omitted variable in most production analysis is the state of technology. There is a lot of variation across provinces in productivity and prices and it seems that the two are correlated:


The first graph shows the price index for aggregate coal input that we constructed. Generally, coal is more expensive in Eastern China. The second graph shows an index of provincial total factor productivity, relative to Shanghai, which is the most productive province. Coastal provinces are the most productive - their distance to the technological frontier is low. To address this potential omitted variables bias, we add province level inefficiency and national technological change terms to the cost function equation. Chirinko et al. (2011) instead used instrumental variables estimation, but we found that their proposed instruments in many cases have very low or negative correlations with the targeted variables. We do use instrumental variables estimation, but this is due to the endogeneity inherent in our constructed coal and energy prices indices. We use Pindyck's (1979) approach to this. We also impose concavity on the cost function, if necessary.

The results show that demand for coal and electricity in China is very inelastic, while demand for diesel and gasoline is elastic. With the exception of gasoline and diesel, there are limited substitution possibilities among the fuels. Substitution possibilities are greater between energy and labor than between energy and capital. These results seem very intuitive to us. However, they are quite different to some previous studies for China, in particular the estimates in the paper by Hengyun Ma et al. (2008) Their estimates of the elasticities of substitution are negatively correlated with ours. Their study uses similar but older data, though we have improved the calculation of some variables. They use fixed effects estimation and don't impose concavity. These might be some of the reasons why our results differ. We also provide traditional fixed effects estimates with concavity imposed. These estimates are mostly close to zero. This suggests that the between and difference estimators are picking up longer-run behavior.

Which of these two estimators should we use in future? We can't give a definitive answer to that question but the difference estimator does seem to have some advantages. In particular, it allows cross-equation restrictions on the bias of technical change, which should result in better estimates of those parameters. So, that would be my first preference, though I am kind of reluctant to ignore the between variation in the data.

Tuesday, January 19, 2016

Influential Publications in Ecological Economics Revisited to be Published in... Ecological Economics

Our paper on the changes over the last decade in patterns of influence in ecological economics has been accepted for publication. Not very surprisingly the journal where it will be published is Ecological Economics. Elsevier have already sent me an e-mail saying that I should expect the proofs on 21 January! That is fast.

Thursday, January 14, 2016

People's Ability to Delude Themselves is Amazing

The Australian reported a couple of days ago that the University of Wollongong gave a PhD for a thesis by an anti-vaccination activist, Judy Wilyman. It's the comments on the article where the delusion is amazing. Many people comment that it is totally outrageous that the University of Wollongong gave this PhD because obviously anti-vax is total nonsense and a conspiracy theory. At the same time, some of them are complaining that climate scepticism doesn't get sufficient respect from academia. Of course, climate scepticism is just as much nonsense and a conspiracy theory as anti-vax.* But these people believe that one of these theories is totally correct and the other totally bogus. I'm a bit surprised, as I thought that both these theories were right-wing anti-government theories. Apparently not in Australia?

This is, of course, exactly the same as people who are convinced that their religion is true and all other religions are false.

* I am open-minded about both anti-vaccination and climate change sceptical hypotheses. Also UFOs, yetis...

Wednesday, January 13, 2016

Between and Within

This will be obvious to anyone with a good understanding of econometrics, but it is quite stunning really to think that all the information you see in the first set of graphs in my previous post on the EKC is thrown away by fixed effects panel estimators. That is because the graphs plot the mean value over time in each country of the dependent variable against the mean value over time in each country of the explanatory variable. Fixed effects estimation first deducts these means from the data and then estimates the regression of the two residuals using ordinary least squares. This is why fixed effects is also called the "within estimator" because the "between (country) variation" you see in these graphs is ignored. Of course, you can estimate a model that just exploits this between variation using the between estimator.*

The reason the latter estimator is rarely used is because researchers are worried about omitted variables bias. Any omitted variables are subsumed in the error term while the fixed effects estimator eliminates their country specific means and so reduces the potential bias. Hauk and Wacziarg (2009), however, found that when there is also measurement error in the explanatory variables (which can also bias the regression estimates) the between estimator performs well compared to alternatives. Fixed effects estimation tends to inflate the effect of the measurement error.

Differenced estimators sweep out any country fixed effects in the differencing operation.** So they also remove all the between variation in the data. However, they do allow us to include country characteristics that are constant over time to explain differences in growth rates across countries, which standard fixed effects does not allow.***

* The linked paper was eventually published in Ecological Economics.
** For a two period panel, fixed effects and first differences produce identical results.
*** There are variations of fixed effects that can allow this.

Monday, January 4, 2016

The Environmental Kuznets Curve after 25 Years

This year marks the 25th anniversary of the release of the working paper: "Environmental Impacts of a North American Free Trade Agreement" by Gene Grossman and Alan Krueger, which launched the environmental Kuznets curve industry. I have a new working paper out whose title capitalizes on this milestone. This is my contribution to the special issue of the Journal of Bioeconomics based on the workshop at Griffith University that I attended in October. It's a mix between a survey of the literature and a summary of my recent research with various coauthors on the topic.

Despite the pretty pictures of the EKC in many economics textbooks, there isn't a lot of evidence for an inverted U-shape curve when you look at a cross-section of global data:


Carbon emissions from energy use and cement production and sulfur dioxide emissions both seem to be monotonically increasing in income per capita. Greenhouse gas emissions from agriculture and land-clearing (AFOLU, lower left) or particulate concentrations (bottom right) just seem to be amorphous clouds. In fact, we do find an EKC with an in sample income turning point for PM 2.5 pollution, but only when we look at changes over time in individual countries. Interestingly, Grossman and Krueger originally applied the EKC to ambient concentrations of pollutants and it is there that it seems to work best.

The paper promotes our new "growth rates" approach to modeling emissions. Here are graphs of the growth rates of pollution and income per capita that exactly match the traditional EKC graphs above:



There is a general tendency for declining economies to have mostly declining pollution and vice versa, though this effect is strongest for energy-related carbon emissions. The graphs for sulfur and AFOLU GHG emissions are both shifted down by comparison. There is a general tendency unrelated to growth for these pollutants to decline over time - a negative "time effect". Growth has a positive effect though on all three. PM 2.5 (lower right) is a different story. Here economic growth eventually brings down pollution. We don't find a significant negative time effect.

I first got interested in the EKC in November 1993 when I was sitting in Mick Common's office at the University of York where I'd recently started as a post-doc (though I was still working on my PhD). He literally drew the EKC on the back of an envelope and asked whether more growth would really improve the environment even if the EKC was true. I did the basic analysis really quickly but then it took us another couple of years to get the paper published in World Development.

Sunday, December 27, 2015

Annual Review 2015

I've been doing these annual reviews since 2011. They're mainly an exercise for me to see what I accomplished and what I didn't in the previous year. I ended last year noting that I had had a full year since I ended being research director at the Crawford School. I didn't know then that I would be taking on another administration/leadership role before the year was over. But, in July, I took over as director of the International and Development Economics Program. So far, this seems to be less work than being research director was and so more compatible with research productivity! In the first part of the year I was chairing the ANU submission to ERA 2015 in economics. The result was disappointing for the ANU, with economics overall falling from a 5 to a 4 as did econometrics (FoR 1403). Applied economics (FoR 1402) fell from a 4 to a 3. We have developed a strategy to turn things around and I am pretty confident we will get a 4 next time. The positive news was that economic theory (FoR 1401) went up from 4 to 5. Also, policy and administration (1605) went from 3 to 5, which was very good news for the Crawford School.


Abu Dhabi
 
Perhaps the best professional news this year is that we got awarded an ARC Discovery Projects Grant for research on "Energy Efficiency Innovation, Diffusion and the Rebound Effect." We are expecting that Zsuzsanna Csereklyei will be joining us next year to work as a post-doc on the project. My colleague Paul Burke also got a DECRA fellowship.

I am also part of a team together with Astrid Kander of Lund University and Sophia Henriques and Paul Sharp at University of Southern Denmark that won a grant from the Handelsbanken Research Foundation on “Energy Use and Economic Growth: a Long-run European Study (1870-2013). The money will mostly fund Sophia and there is some additional  travel money. As I won't be traveling to Sweden in the near future (see below), it looks like Akshay Shanker - one of our PhD students - who I am working with on a directed technological change paper - will use the money to travel to Sweden early in 2016.

Punting on the River Cherwell, Oxford
 
In July, I traveled back to the UK after returning to Australia from conferencing in the Middle East (see below). I attended a brainstorming workshop at Oxford Policy Management (in Oxford, of course, at Pembroke College) to prepare a proposal to get funding for research on electricity and economic growth and development from the UK, Department For International Development. At this point, it looks likely that our consortium will get the grant but this isn't confirmed yet.

Pembroke College, Oxford

We got four journal articles accepted for publication including our papers on carbon dioxide emissions in the short-run in Global Environmental Change and on global energy trends in Energy Economics, and articles in: Environmental and Resource Economics (still "in press") and the Journal of Cleaner Production (January 2016 publication date). In the meantime, our Energy Journal paper accepted in 2014 is still in press and doesn't yet show up on the journal website.... I also released four working papers that aren't yet published: Two with Stephan Bruns - one on research assessment using citations and another on meta-analysis of Granger causality test statistics, a third one with my former masters student Luis Sanchez, and the fourth one with a long list of coauthors headed by Bob Costanza. We have received revise and resubmits for the latter two and resubmitted the papers. I have another paper coauthored with Chunbo Ma where we also received a revise and resubmit that we are now working on. When we do, we'll also put out a working paper. We also did a revise and resubmit on a paper submitted in mid 2014, which is now under second review. I now have a spreadsheet to help keep track of all these projects!

Right now, I have ten publications in various stages of the review and publication process. Two are in press, three resubmitted after revision, two we are revising, and three in first review.  First review at that journal - we've already sent one to a bunch of other journals.

I also published two book chapters. One is an article on the energy GDP relationship in the New Palgrave Dictionary of Economics and the other a chapter in a Routledge book on energy and poverty.

One milestone this year was passing 10,000 citations on Google Scholar and an H-Index of 40. I also just went over 4,000 citations on Scopus.


Champagne Pool, Waiotapu Thermal Area, near Rotorua

I went to the AARES conference in Rotorua in February, the IAEE meeting in Antalya, and for the first time to the International Energy Workshop, which was in Abu Dhabi. I also gave a seminar at University of Queensland in September and was invited to a workshop at Griffith University in October. Finally, I went to the Economics and Business PhD Conference at UQ in early November to comment on a PhD student's paper. Locally, I moved house and suburb in Canberra, buying a house for the first time in my life.

Since August, Donglan Zha has been visiting Crawford from Nanjing Aeronautics and Astronautics University. We are going to work on modeling concentrations of air pollution in China. I also have a new PhD student since the beginning of the year, Panittra Ninpanit. Her first PhD paper will be on decomposition of carbon emissions in Thailand using input-output analysis.

I taught the quantitative methods section of our environmental management research methods course over five weeks in the first semester. This is a tough subject to teach in such a short time slot. I thought I did well, but I got my worst evaluations so far at Crawford School. I guess most people don't like doing statistics. I also taught my energy economics course again and will continue to teach it in the future. It has been rebranded as an economics course, IDEC8089, instead of a general Crawford School course (CRWF8017). This doesn't seem to have affected participation from across different ANU programs too much.

Ecological Economics has gone to a new editorial model where there are several editors who handle much of the incoming flow of paper submissions and associate editors like me play a lower key role. I was offered to be one of the new editors, but I decided that the cost/benefit trade-off wasn't good enough and after 13 years (!) as an associate editor it was time for others to play a bigger role. I have joined the editorial advisory board for Nature Energy, a new journal that will start publishing in 2016.

As I am getting more involved in Twitter, I posted fewer blogposts this year - only 38. The most popular was: "The Industrial Revolution Remains One of History's Great Mysteries?" Second was:
"The Extent and Consequences of P-Hacking in Science" and third: "Carbon Dioxide Emissions in the Short Run: The Rate and Sources of Economic Growth Matter".

As always, it is possible to predict some of the things that will be happening in the coming year, though this year is more uncertain than most. First, I'm not sure how long I will be IDEC director for.  Our main innovation in the program that we hope happens in 2016 is a new degree targeting the private fee-paying market for masters degrees (rather than scholarship funded). I'll let you know more if it is successful. Second, my wife is expecting a baby due on 5 February. So, I haven't submitted any abstracts to conferences as I normally would.... We will see how things go.

On the predictable side, I hope to put out three new working papers early in the new year. Two will be the last two papers from our DP12 ARC grant. One is the paper coauthored with Chunbo on estimaing elasticities of substitution and the other the paper on the industrial revolution coauthored with Jack Pezzey. All the math for the latter paper is now nailed down and it is just a question of polishing. Another will be based on a paper I just submitted to the Journal of Bioeconomics for a special issue based on the Griffith workshop. As mentioned above, Zsuzsanna Csereklyei should be moving to Canberra in early 2016 to start work on the ARC grant.

Backyard at our new house

Sunday, November 15, 2015

Wrapping up ARC DP12 Project

I just submitted the final report for this funded project which has been running since 2012 to the research office. We achieved most of the project goals despite receiving much less funding than requested. I also had to take on the role of research director for the Crawford School for 2 years of the project, which took up quite a lot of my time.

On the other hand, one of the main papers is still not quite complete and another is in the revise and resubmit stage. We haven't yet put out working papers for either of those papers either. So, the reduced funding and added admin work did slow things down. So far we have published the following papers that credit the ARC for funding:

Lu Y. and D. I. Stern (in press) Substitutability and the cost of climate mitigation policy, Environmental and Resource Economics. Working Paper Version | Blogpost

Csereklyei Z., M. d. M. Rubio Varas, and D. I. Stern (2016) Energy and economic growth: The stylized facts, Energy Journal 37(2), 223-255. Blogpost

Kander A. and D. I. Stern (2014) Economic growth and the transition from traditional to modern energy in Sweden, Energy Economics 46, 56-65. Working Paper Version | Audioslides | Blogpost

Bruns S. B., C. Gross, and D. I. Stern (2014) Is there really Granger causality between energy use and output? Energy Journal 35(4), 101-134. Working Paper Version | Blogpost

Stern D. I. and K. Enflo (2013) Causality between energy and output in the long-run, Energy Economics 39, 135-146. Working Paper Version | Blogpost

As we are still completing what I think is the most important paper of the project, on the industrial revolution in Britain, this story is definitely not complete yet. In retrospect, I probably should have asked for an extension of the project at the end of last year, so that we could put in a more complete final report to the ARC next year, rather than this year.

Tuesday, November 10, 2015

Really, What is the NBN For?

What I mean is, why do we need a new government network in urban areas? We just got a "set top box" for streaming Chinese TV channels. My mother-in-law is going to be visiting :) It operates via wifi from our Telstra "modem". TV is better than reception of free Australian channels so far. Of course, there are lots of such services from Netflix etc. which seem to work in Australia without major problems. Maybe an RBN (Rural Broadband Network) is what the government should be focusing on?

Superannuation Reform

I started writing this on Twitter but it got too long :) Peter Martin proposes taxing superannuation contributions at ordinary income tax rates and then not taxing earnings or payouts of superannuation funds. This would greatly simplify the superannuation system and is the logical progression of Costello's introduction of tax free superannuation pensions and the recent move to increase the contributions tax people earning more than $300k p.a. It is equivalent to the U.S. Roth IRA. It could, in theory make running a self-managed super fund as simple as having an ordinary brokerage account (as it is in the U.S.) as the funds wouldn't owe tax.

There is one drawback, though. Taxing up front, leaves less capital to accumulate and so super payouts and the tax collected will be smaller than if instead we followed the U.S. 401k model. This is where payouts are taxed at regular income tax rates and contributions and earnings are tax free.* But, at this point, this would be a more radical change than the Roth IRA route. Existing superannuants would have to be grandfathered or they would complain about double taxation compared to current contributors. So, it's more likely we go down the Roth IRA route.

Most likely, of course, is a relatively minor change that complicates the system further or doesn't reduce the complication such as reducing the contributions tax concession to 15% across the board. Or eliminates the up-front concession but doesn't eliminate taxing superannuation earnings.

* There are probably some equilibrium effects that reduce the difference between the two....

Thursday, November 5, 2015

Hatfield Dodds et al. Nature Paper

Steve Hatfield-Dodds has published a paper today in Nature with many other CSIRO colleagues titled Australia is ‘free to choose’ economic growth and falling environmental pressures. It is the result of a integrated assessment modeling analysis of Australia and the global economy under a variety of climate policy and other scenarios.

Steve comments on the paper:

"“Our key finding is that Australia can break the links between economic growth and environmental pressure, with key pressures falling or stable while the economy more than doubles in size out to 2050.  This can be achieved through mobilising proven technologies through extensions of established policy approaches.  Our analysis suggests other countries can also ‘decouple’ economic growth from environmental damage.

We do not find, however, that environmental pressures can be reduced for free.  In most cases, reducing environmental pressure results in economic growth being a little slower than it would be in the short term, but then stronger in the long term.  In some cases – like energy efficiency – reducing environmental pressure results in stronger economic growth almost immediately.

But perhaps the most striking aspect of the results is that very large reductions in environmental pressures – including reversing the loss of native habitat in our agricultural landscapes, or achieving zero or lower net greenhouse gas emissions – have relatively modest impacts on income and living standards, whether the impacts are positive or negative.

The analysis represents a number of scientific advances, accounting for multiple aspects of resource use and environmental performance, and locating these in the context of economic activity and growth.  This allows us to explore the relationships between essential services humanity derives from nature, including energy, food, and clean water, and the environmental footprint of these services.

The analysis also explores the different kinds of choices involved in shifting towards a more sustainable future.  We find that while individual choices by businesses and households make an important contribution, policy choices are crucial.  We also find that changes in social values are
not required to make progress towards sustainability over coming decades.”

By contrast, a News and Views article in the same issue of Nature by Benjamin Bodirsky and Alexander Popp suggests that a better way forward would be " investing carbon-tax revenues in education and science, establishing markets for flexible electricity consumption, providing bicycle and public transport infrastructure and promoting healthy and sustainable diets." They argue that then less strict regulation would be needed to keep the economy within environmental boundaries. While I think this could help, I don't think it is likely to make a major contribution to the change needed by 2050.

I was asked to provide expert comment on the Hatfield-Dodds paper for a press release. I commented:

"“The paper by Hatfield-Dodds et al. is similar to many existing studies including those reviewed in IPCC reports using Integrated Assessment Models, which are simulation models of the economy and environmental impacts that result from economic development and climate policies. They claim that they include more environmental impacts and indicators than previous research.

They simulate various scenarios including existing trends where current climate policies continue both globally and in Australia and a no climate policy scenario, which they call "material intensive" and strong climate policies globally and in Australia.

In common with most existing mainstream studies they find that strong policies to abate greenhouse emissions do not prevent economic growth. This is in contrast to what they call "Communitarian Limits" approaches like Tim Jackson's book "Prosperity Without Growth" that claim that economic growth must stop in order for society to have a chance at dealing with climate change.

The surprising finding in the paper is that there are scenarios where the economy doesn't just continue to grow under a strong climate policy but that income per person is actually higher than under current trends - "Win-Win". This seems to be because Australia gains from changes in the global economy under the strong climate policies. For example, other countries pay to plant trees in Australia to capture carbon dioxide.”

Friday, October 30, 2015

Discovery Projects 2016

We - myself together with Stephan Bruns and Alessio Moneta - got an ARC Discovery Projects grant. Thanks also to Zsuzsanna Csereklyei who contributed to the development of the proposal and who we may hire as a post-doc using the grant - depending if she wants to come to Australia for the time we will be able to afford to fund with the money we received ($A273k - 65% of what we requested). This is my second ARC grant following the DP12 grant that we got a few years ago. The title of our project is: "Energy Efficiency Innovation, Diffusion and the Rebound Effect". We will be looking at the diffusion of energy efficiency innovations and trying to measure the economy-wide rebound effect empirically. This was our second attempt at applying for a grant on this topic. Last time around we were rated in the top 10% of unfunded proposals and so I thought it was worthwhile revising and resubmitting!

Other good news today is that my colleague, Paul Burke got a DECRA grant. I think this is our fourth DECRA at Crawford. Congratulations to Paul! Also Peter MacDonald and Robert Sparrow got a DP16 grant. Congratulations to Robert and Peter!

Google Scholar Matures

Since it was introduced in late 2004, Google Scholar has rapidly grown to become a widely used tool for finding and assessing the impact of academic literature. The database still suffers from noise relative to its competitors Scopus and Web of Science but it has broader coverage, especially in the social sciences and humanities and is open access. As the database developed, Google have periodically added new information sources to the database. This resulted in a rapid growth in estimated citations of articles in the early years. However, it now seems that the database has matured. The following graph shows the growth rate of citations to my research in the previous 12 months, measured monthly since 2009 for Google Scholar in blue and a bit more intermittently for Scopus in red. I have also fitted exponential trend lines to the two series:

Initially the growth rate of Google Scholar citations was very high and very erratic. But the month to month variation in the annual growth rate has reduced drastically over time. By contrast, the growth rate of Scopus citations has been much more consistent, with a slow rate of decline in the percentage growth rate over time. Interestingly, the two series have also converged to a common growth rate of 17-18% per year. So, it seems that Google's database is now as mature as Scopus is. This doesn't mean that Google is now as high a quality data source as Scopus is. It isn't. But large revisions to citation counts or additions of large new data sources seems to be a thing of the past.

Tuesday, October 20, 2015

Business as Usual Emissions Projection from Sanchez and Stern Econometric Model

I finished preparing my presentation for Thursday in Brisbane. The topic of my talk is "Drivers of Industrial and Non-Industrial Greenhouse Gas Emissions". It's mostly based on my paper with Luis Sanchez. I'm also adding some material from Chapter 5 of the IPCC AR5 report (WG3) to give context. This is because this "trends and drivers" research theme came out of my work on the IPCC chapter. Reyer Gerlagh produced our original "iconic image" (yes, we called them that in the IPCC process) of the long-run growth rates of emissions and income per capita and then I suggested to do an econometric analysis along those lines. I think it was Reyer also who suggested how to model the EKC in a growth rates model.

I've also "added some value" by doing a business as usual projection using our model. This is something we are thinking to do as part of the revise and resubmit for a related paper. The graph shows projections to 2030 for 3 developing and 3 developed countries and the world (well, our 129 country sample) as a whole:


Indonesia and India have similar income per capita, so an EKC model would project similar emissions growth in both countries. The graph shows the value added of our model, which suggests that emissions will grow slower in Indonesia, which is more emissions intensive. The global outcome is similar (a little bit higher) to RCP 8.5, which is the highest emissions growth scenario used in AR5. RCP 8.5 assumes slower economic growth than we are here but slower than historic progress in energy intensity.

To get the projection, I used our model parameters estimated for the 1991-2010 period and the UN median projection for population growth. I used USDA ERS projections for economic growth rates in each country. Other variables are at their values for 2010.

Monday, October 19, 2015

Managing the Transition to a Sustainable Economy


On Thursday morning at 9:35am I'll be presenting at the Managing the Transition to a Sustainable Economy Conference at Griffith University in Brisbane. I'll be presenting my paper on Drivers of Industrial and Non-Industrial Greenhouse Gas Emissions. This is a slight change from the original paper I was supposed to present, as that got published in the meantime, and the organizers only want unpublished research. I blogged about the paper in March. Right after me, John Foster is speaking.  John Gowdy from my former university RPI is also speaking at the conference. The full schedule is here.

Monday, September 28, 2015

Influential Publications in Ecological Economics Revisited

Back in 2004 I published with Bob Costanza, Chunbo Ma, Brendan Fisher, and Lining He a paper that looked at the most influential publications on the field of ecological economics. Then, about this time last year Gaël Plumecocq contacted me about participating in a session he was organizing at the European Society of Ecological Economics meeting in Leeds on "ecological economics understood as an epistemic community". I had the idea of revisiting our 2004 paper a decade later and seeing how the field had changed in the meantime. Eventually, Gaël also came on board our author team, contributing a textual analysis of the key themes in the influential papers. Gaël gave a presentation on the paper at ESEE and now we finally have a working paper version of our new paper on the web. The full author team includes: Bob Costanza, Rich Howarth, Ida Kubiszewski, Shuang Liu, Chunbo Ma, Gaël, and myself.

We downloaded from the Web of Science (WoS) information on all the papers published in Ecological Economics from 2004 to 2014 including the number of citations each received and the full reference list from all 2960 articles. We define outwardly influential papers as the 10% of articles published in the journal in each year from 2004 to 2014 that received the most citations in the Web of Science. The inwardly influential publications are all publications that received more than 15 citations in the journal in the period 2004-2014. For each of these publications we collected the total number of citations in the Web of Science, Google Scholar, and Ecological Economics. The inward influence data needed a lot of cleaning up, which was mainly done by Chunbo and Ida with my help.

Shuang produced these graphs of inward and outward influence using Tableau:




For inward influence, there are many publications at the bottom right that have been relatively much more influential across science as a whole than they have been in ecological economics. Publications towards the left have been mostly influential in ecological economics alone. By contrast, there is a stronger correlation between citations received in the journal and more broadly for the outwardly influential articles. One outlier is the Pimentel et al. paper on the costs of invasive species that is the most cited article (by WoS cites) ever published in ecological economics.

The theme analysis found, as we expected, that the most influential topic was ecosystem services and payments for ecosystem services, which received 25% of the citations of the influential publications. By contrast, sustainable development and foundations of ecological economics were the most influential topics prior to 2004.

We also followed up on my 2006 paper with Chunbo Ma by looking at the journals, which cite Ecological Economics the most and which are cited by Ecological Economics the most:


There have been quite dramatic changes in these lists with more than half the journals being new entrants. In general there has been an increase in citation links to interdisciplinary environmental science and environmental studies journals and a reduction in links to mainstream economics journals including environmental economics journals. No general interest economics journals are now on the top 20 inward and outward lists.

We think that these trends reflect a maturation of ecological economics as a transdisciplinary field.

Wednesday, September 23, 2015

Nature Energy

I have joined the editorial advisory board for Nature Energy, a new journal from the Nature Group that will begin publishing at the beginning of 2016. The position involves giving feedback on submitted manuscripts, but I can also make suggestions for commentary and news and views articles. The latter are a special feature of Nature journals that provide less technical overviews of articles published both in Nature journals and other academic journals. I would appreciate any suggestions you might have for upcoming articles that the journal might cover in news and views, or topics/authors for commentaries.

Thursday, August 27, 2015

Global Energy Use: Decoupling or Convergence Accepted to be Published in Energy Economics

My paper with Zsuzsanna Csereklyei on trends in global energy use and whether they can be better explained by decoupling or convergence in energy intensity or some mixture has been accepted to be published in Energy Economics. I wrote a blogpost about the paper in December last year when we first completed the paper.

This was not a bad review experience though Zsuzsanna who is in a short-term post-doc position would have liked it to be faster! We first sent the paper to World Development who desk-rejected it. Then we sent it to Energy Economics. The first review took seven months due to one of the referees dropping out due to family health problems and then the journal needed to get another referee. We turned around the paper in 12 days and then got a conditional acceptance a month later. We turned that around in one day and got the final acceptance a day later. This paper applies the method developed in Anjum et al. (2014) to energy and also adds treatment of spatial autocorrelation. The whole process of writing and publishing this paper took place while Anjum et al. has been in review...

Update 5 October

The journal also got the final version of the paper with page numbers onto the web incredibly quickly following us returning the final proofs.