Numbers for Pascal: Explaining differences in theestimated benefits of the Doha Development Agenda

Economists use partial and general equilibrium trade simulation models toestimate the impact of changes in domestic policies and international trade rules.During the WTO Doha Development Agenda (DDA) negotiations economists haveproduced many different estimates of the gains that would result from global tradeliberalisation scenarios. However, these estimates differ quite widely even forapparently similar liberalisation scenarios. The result is confusion about the truemagnitude of the gains from trade liberalisation, and a reduction in the perceivedcredibility of the theories and models that economists use. We apply meta-analysis to adataset extracted from 110 studies that present simulated assessments of global tradeliberalisation scenarios under the DDA. Initial meta-regression analysis demonstratesthat covariates that capture model characteristics, the nature of the data used in themodelling exercise, and the nature of the simulated liberalisation scenarios can explainroughly one-third of the variance in the dependent variable ‘simulated global welfarechange’. We test whether additional explanatory power can be obtained by addinginformation about the authors of the simulation studies. We find significant fixedeffects for the top 20 authors in the field. We interpret this as evidence that leadingauthors in the field employ model specifications that reflect their individual preferencesand beliefs about how economies function and the impact of liberalisation,specifications that are hidden in the complex interactions of simulations models andtherefore difficult to capture in a meta-analysis. We use these results to generate aconfidence interval for the gains that would result from trade liberalisation under theDDA.