Based on a quantitative meta-analysis of empirical studies, this article points out a significant flaw in the Three Worlds of Welfare literature, the “variable selection problem.” Compiling, classifying, and quantitatively analysing all variables that have been employed in this literature, the article shows first that variable selection has depended more on case selection than on theory. Scholars tend to employ variables based on data availability, rather than selecting variables according to theoretical frameworks. Second, the use of welfare policy variables is mostly limited to the analysis of Organization for Economic Co-operation and Development (OECD) countries, while studies analysing non-OECD countries, where data is limited, tend to use developmental outcome variables as a proxy. This tendency harms conceptualization and operationalization of welfare regimes, as well as blur the boundary between development and welfare regimes studies. Third, the use of original Esping-Andersen variables remains very limited, undermining continuity, comparability, and reliability within the literature.