Using the stylized U-shaped trend as an empirical selection criterion for homophily measures

Quantifying intergenerational changes in educational homophily is challenging when education level of marriageable individuals is generation-specific. To address this challenge, the literature proposed various indicators. We argue that suitable indicators should meet several analytical criteria. However, our main criterion is empirical in nature: suitable indicators, when computed from data on American couples born after 1930, should exhibit a U-shaped trend at the national level and for the majority of the US states. A cardinal homophily indicator constructed with the NM-method, based on an old forgotten and recently reinvented ordinal indicator, is one of the few indicators that meets the criteria.