Construction of the database

The meta-analysis begins with the construction of a database including the primary relevant studies. A resolute emphasis has to be placed on including all studies, published or not, as a way of reducing potential selection bias introduced by a nonrandom selection of studies. A typical database has to include publication details, the estimates of the effects sizes and information about its distribution, estimation characteristics and background variables such as the type of data used or the time period on which the study pertains. Even if the construction of a database on EKC primary studies does not necessitate much theoretical consideration, it does face, in practice, several difficulties.

As explained earlier, the most obvious difficulty is to get access to the whole body of pertinent empirical studies on the EKC. In order to avoid a possible nonrandom selection of studies, we conducted an extensive bibliographical research on the EKC. We therefore used several research databases (Econlit, Dissertation Abstracts, RePEc¹⁹ and JSTOR), we also consulted the websites of economic review editors (ELSEVIER, Kluwer, etc.) and of international organizations (World Bank, OECD, UNO, and WTO). We also used standard Internet research tools such as Scirus and Google.

Finally, the bibliography of literature reviews conducted on the EKC completes our search. In each enquiry, we used several keywords such as “growth and environment”, “inverted U curve” and

“environmental Kuznets curve”²⁰. We selected in each case the entire set of available years (until December 2002).

Fig. 2.I Selection procedures (Adapted from ANAES, 2000)

Overall, more than 200 sources were found. This first list contained published and unpublished as well as empirical and theoretical work. In order to select the pertinent empirical literature on the EKC, we followed a selection process composed of three steps. Figure 2.I presents the latter.

First, we examined the title, abstracts and keywords of each study. This allowed us to check all the purely theoretical work and to focus only on studies that offer empirical evidence on the EKC.

Secondly, we examined the empirical estimations available in each study. At this stage, we rejected

19 Research Papers in Economics

20 One may note that the term Environmental Kuznets curve is not an adequate keyword for pinpointing the earliest studies as they do not refer to it in this manner. Indeed, the original studies examining the relationship between environmental quality indicators and GDP per capita used the term inverted U curve.

1) Title, abstract, keywords Empirical studies on the relationship between economic

affluences and environmental quality

2) Existence of results Satisfactory statistical details

3) Detailed reading Selection criteria

NO

NO

NO

Excluded studies

YES

YES

Unavailable work

YES

Included studies

studies presenting incomplete statistical results. Our database reduced to 67 primary studies composed of published papers, working and discussion papers as well as PhD dissertations. Finally, we carefully read the available studies and rejected part of them in order to preserve the homogeneity of our database. For this last cut, we adopted the following criteria.

• The primary studies examining time series evidence (i.e. examining the pollution path of one individual country through time) have been excluded. The following reasons justify this choice.

First, as these studies examine only one country, they do not address the general occurrence of the EKC relationship. Furthermore, time-series estimates are not comparable to the ones issued from the majority of studies that use panel or cross-countries data. Overall, 8 primary studies have been omitted.

• Secondly, we considered only the studies based on one of the 6 econometric specifications presented in chapter 1 (quadratic and cubic specification in level or logarithm). Therefore, the observations relying on non-parametric analyses in Amazohou et al. (2001), the observations of Bradford et al. (2000) based on the BSS specification and those of Galeotti et al. (2001) based on Weibull and gamma specifications have been excluded (see chapter 1, section 3.1).

Once again, the impossibility of properly comparing them with the rest of the literature explained this choice.

• Finally, we rejected some observations that examine very particular types of pollution. For example, Heerink et al. (2001) is the only study that examined the concentration of phosphorus and nitrogen nutrients in the soil of sub-Saharan countries. As pollution type tends to influence the pollution-income path observed, the meta-regression has to control for the pollutant considered in primary studies. We therefore rejected these «isolated» observations in order to limit the number of moderator variables.

Tab. 2.1 Rejected observations

Studies excluded Causes of exclusion

Tharakan et al. (2001) Times series analysis of China, India, Indonesia, Japan and Pakistan, lack of statistical information

Shafik and Bandyopadhyay (1992) Replicated in the study of Shafik (1994) Roberts and Grimes (1997) Lack of statistical information

Unruh and Moomaw (1998) Lack of statistical information, the study is based on a graphical analysis (phase diagram) Egli (2002) Time series analysis of Germany

Lindmark (2002) Time series analysis of Sweden Mhenni (2002) Time series analysis of Tunisia Roca et al. (2001) Time series analysis of Spain Lim (1997) Time series analysis of South Korea

Raymond (2004) Unique study using the environmental sustainability index as an indicator of environmental quality

Heerinks et al. (2001) The observations on nitrogen and phosphorus in the soil are rejected This is the only study using those indicators.

Cole et al. (1997)

The observations on methane emissions are rejected This is the only study using this indicator. Furthermore, methane emissions are mainly due to non-anthropic causes (fermentation) and therefore are a very poor indicator of pollution due to economic activities.

Frankel and Rose (2002) Observations on energetic losses are rejected Galeotti and Lanza (1999) Weibull estimations are rejected

Bradford et al. (2000) BSS (named after authors’ initials) estimations are rejected Amazohou and Van Phu (2001) Non-parametric estimations are rejected

Shi (2001) Observations on total pollution instead of pollution per capita or concentration are rejected.

Levinson and Hilton (1998) Observations on lead emissions in the air are rejected.

Hauer and Runge (2002) Lack of statistical information

Barbier (2004) Observations on total agricultural area are rejected.

Table 2.1 presents the rejected observations. However, the latter will not be completely omitted since we will compare their findings with the conclusions emanating from the meta-analysis later on (see section 4.5).

Another obvious difficulty we faced throughout the literature retrieval process was to access to a concrete paper version of the references found. Usually, primary studies are easily accessible.

However, some references have not been found either because the working paper series was exhausted or their authors could not been contacted²¹.

Overall, the final database counts 49 studies (from 1992 to 2003) emanating from 44 researchers or group of researchers. 72% of them are published²². These 49 studies offer overall 286 observations on the EKC. Figure 2.II presents their time distribution.

1

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Observations Studies

Fig. 2.II Empirical studies and observations on the EKC