The scope of meta-analysis for transport policy impact analysis in environmental economics

Abstract

Meta-analysis offers an analytical framework for research synthesis based on a comparative study of research findings undertaken by different researchers. In this paper, we investigate the possibilities of applying meta-analysis to transport policy impact studies in environmental-economics. The heterogeneity of studies in this field however makes it difficult to apply meta-analysis directly. We therefore propose a general equilibrium framework as a benchmark for comparison, and as a synthesis of the research findings we obtain from studies underlying a met a-analysis. A meta-analysis of studies results in decision rules that obtain the environmental impact of a transport policy as a function of the characteristics of these studies, i.e. variations in environmental impact of the transport policy can be attributed to variations in specific characteristics of these studies. The transport policy impact studies underlying a meta-analysis in environmental economics can be seen to derive their characteristics from a common general equilibrium framework. This framework leads to a classification of all possible characteristics of transport impact studies, that can be used as a basis for several types of meta-analytic methods to distinguish the most relevant ones among them. Policy makers can then improve the effectivity of their policies by concentrating on these relevant characteristics. 1 Meta-Analysis in Environmental Economics In the past decades many advances have been made in the social sciences by applying principles from met a-analysis. Meta-analysis is a research methodology that serves to bring together in a succinct and systematic way findings from previous research on a given issue or topic, undertaken by different researchers. Thus, the main aim of meta-analysis is to offer an analytical framework for research synthesis, usually based on comparative case study research. This approach has gained quite some momentum in environmental economics and related disciplines (see for a review and applications, van den Bergh et al. (1997)). The popularity of meta-analysis in environmental economics is caused by two factors: (i) meta-analysis is particularly useful in case of comparison of behavioural or policy outcomes that are not reflected in the ‘measuring rod of money’; and (ii) meta-analysis can also be applied in case of qualitative effects of decisions or actions, a situation which is often present in case of environmental phenomena. The complexity of environmental economic phenomena is often rather high. Even in cases where monetary valuation is applied (e.g., in social cost-benefit analysis) the research efforts are often so high, that an easy application in other cases is often prohibitive. This has prompted the development of value transfer methods, which aim to translate research findings to other, comparable case studies (see Bal and Nijkamp (1998)). In recent years also various applications of meta-analysis to transport economics in relation to environmental economics can be observed, for example, on the comparison of price elasticities in public transport (see e.g., Nijkamp and Pepping (1998)). But as a whole, applications in this field are still scant, although there might be quite some potential for fruitful applications. An important research question is now whether it is possible to develop a research methodology that can act as a general framework for the application of meta-analysis studies at the interface of transport economics and environmental economics. This is once more important, as meta-analysis is generally shifting its meaning from a rather narrowly defined statistical approach to a general approach for comparing findings of different studies on similar topics or issues, not only empirical, but also theoretical and methodological. In the present paper it will be argued that a general equilibrium approach, including externalities and transportation, may offer such a comprehensive methodology framework. The structure of this paper is as follows. First, the changing scene of transport will be sketched (Section 2). Then the relation between transport, land use and economic activities will be outlined (Section 3). In the next section (Section 4) the foundations of a general spatial-economic equilibrium framework including the environment will be laid down. Section 5 will then be devoted to a classification of transport impact studies, while analytical approaches for comparing such impact studies will be outlined in Section 6. The paper will be concluded with some pressing research questions in Section 7. 2 Current Trends and Issues on Transport and the