The Missing Main Effect of Welfare State Regimes: A Replication of 'Social Policy Responsiveness in Developed Democracies' by Brooks and Manza

This article reports the results of a replication of Brooks and Manza's "Social Policy Responsiveness in Developed Democracies" published in 2006 in the American Sociological Review. The article finds that Brooks and Manza utilized an interaction term but excluded the main effect of one of the interacted variables. This model specification has specific implications: statistically, that the omitted main effect variable has no correlation with the residual error term from their regression; theoretically speaking, this means that all unobserved historical, cultural, and other characteristics that distinguish liberal democratic welfare regimes from others can be accounted for with a handful of quantitative measures. Using replicated data, this article finds that the Brooks and Manza models fail these assumptions. A sensitivity analysis using more than 800 regressions with different configurations of variables confirms this. In 99.5 percent of the cases, addition of the main effect removes Brooks and Manza's empirical findings completely. A theoretical discussion illuminates why these findings are not surprising. This article provides a reminder that models and theories are coterminous, each implied by the other.