Whilst the extant literature suggests the size of district magnitudes (DMs) positively influences women's descriptive representation in theory, both causal identification and the causal mechanism of the effect of DM have yet to be examined rigorously. This paper proposes a novel mechanism via which larger DM increases women's representation under personalised electoral rules, and investigates this mechanism with a difference-in-differences design on an original dataset from Japanese local elections, which use Single Non-Transferable Vote (SNTV) with varying DMs and where women are notoriously underrepresented. The empirical findings largely support the anticipated level of electoral competition as an important causal channel linking DM size and women's candidacies. As political experience at the local level is often a crucial step in political careers in many democracies, the findings will likely have implications on women's representation to numerous polities employing less party-centred electoral systems at the national or subnational level.
