Historical trend in educational homophily: U-shaped or not U-shaped? Or, how to set a criterion to choose a criterion?

TL;DR

This paper reviews and evaluates criteria for measuring educational homophily and inequality over time, proposing a robust indicator to analyze historical trends in educational assortative mating.

Contribution

It introduces a set of analytical and empirical criteria for selecting suitable homophily indicators and identifies a specific indicator that meets all criteria for analyzing educational inequality trends.

Findings

A specific cardinal indicator satisfies all criteria.

Many common indices fail to meet the criteria.

The proposed indicator can be applied across countries with available data.

Abstract

Measuring changes in overall inequality between different educational groups is often performed by quantifying variations in educational marital homophily across consecutive generations. However, this task becomes challenging when the education level of marriageable individuals is generation-specific. To address this challenge, various indicators have been proposed in the assortative mating literature. In this paper, we review a set of criteria that indicators must satisfy to be considered as suitable measures of homophily and inequality. Our analytical criteria include robustness to the number of educational categories distinguished and the negative association between intergenerational mobility and homophily. Additionally, we also impose an empirical criterion on the identified qualitative historical trend in homophily between 1960 and 2010 in the US at the national and sub-national levels. Our analysis reveals that while a specific cardinal indicator meets all three criteria, many commonly applied indices do not. We propose the application of this well-performing indicator to quantify the trend in overall inequality in any country, including European countries, with available population data on couples' education level.