Do not use inferential statistics to evaluate quality of matching

Quantitative research in bilingualism often involves between-group comparisons in the presence of on one or more potentially confounding variables. There is no risk of confounding if the potential confounders are matched between groups. But when is a variable sufficiently matched? A common approach to assessing the quality of matching is to apply inferential statistics to the variable(s). In this paper, I argue that this approach is theoretically and practically problematic, and that there is no purely quantitative, objective alternative. Matching quality can only be evaluated by a comparison of the sample distributions, informed by expert knowledge about the research topic.