The proposed study will assess competing explanations of adoption of proportional parliamentary representation (PR) between 1899 and 1920. This will be done by combining nation-level statistical analysis with a study of cases. Emphasis will be on the case s, asking whether or not the causal mechanisms assumed in statistical studies appear to be present, and thus whether the explanations suggested find support using more fine-grained methods. By looking at the causes of PR, the study should be of relevance to studies of the effects of electoral formulas, and consensus democracy in general. It will aim to make its implications explicit and conduct very limited re-analyses of earlier statistical studies.