How diverse are political institutions? Despite the theoretical and political relevance of this question, there is no standard measure of diversity in political institutions, which hinders systematic research on patterns of diversity around the world. This letter introduces a Diversity of Representation Index (DORI), a measure of diversity considering multiple sociodemographics and their fair representation. Moreover, I provide the first comprehensive data on descriptive diversity in parliaments in 28 Western democracies from 1789-2020 in terms of age, gender, and race and ethnicity. I first show that sociodemographic diversity has been low throughout the period, but has increased since the 1960s due to the inclusion of historically underrepresented groups. Then, drawing on applications in various fields, I demonstrate the importance of studying diversity in political science research and how DORI represents a unified yet multidimensional and flexible measure to assess it.

What determines the level of minority descriptive representation in the U.S.? District racial composition and electoral system are considered key to minority representation, however, the exact influence of different electoral systems at varying levels of minority population is still unknown. We introduce a unified theory of minority representation that reconciles the two camps of research based on quantitatively predictive logical models. Moreover, we present an alternative approach to measure minority descriptive representation and the effect of different electoral systems on it. Using data on US House and state legislative elections we predict the emergence and success of minority candidates under At-Large, single, and multi-member districts electoral systems and in (non)majority-minority districts. Finally, we reanalyze extant studies on minority descriptive representation, demonstrating how our approach can ascertain the effects of other factors after accounting for electoral systems and racial composition.

How does candidate gender affect voter preferences under the traditional model of spatial competition? Although prior work shows that voters tend to have biased perceptions of ideological positions and issue expertise when comparing female and male candidates, we do not yet know how these perceptions ultimately influence vote choice in a proximity framework. We argue that voters are confronted with a trade-off involving (i) candidate gender, (ii) ideological distance (proximity considerations), and (iii) policy issues (valence considerations). We disentangle the interplay of these three factors by using a survey experiment and by re-analyzing existing survey experiments which neglected candidate gender as an otherwise unimportant control variable. The results help us better understand the interplay of candidate gender and proximity voting as well as the advantages and disadvantages that female politicians face when running for office. As such, they contribute to a lively literature on gender gaps in voter perceptions as well as voting preferences and vote choice.