How diverse are political institutions? This is a recurrent question in the representation literature and in recent political debates. Despite its importance, there is no standard measure of diversity in political institutions and no systematic information on patterns of diversity in parliaments around the world. This article introduces a Diversity of Representation Index (DORI) and presents novel yearly 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 marginalized groups. I then demonstrate how DORI provides new insights in various fields, such as the study of ideological diversity, electoral institutions, and the welfare state. DORI stands as a unified yet multidimensional and flexible measure of diversity ready to be incorporated into standard research.

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.