On the measurement of non-random mating and of its change over time

This paper proposes a new approach to the measurement of assortative mating and of the change over time in assortative mating. Non-assortative mating is viewed as independence between the characteristics of the husband and those of the wife. In our paper the characteristic we focus on is the educational level of the spouses. In measuring the change in assortative mating we use an algorithm that allows one to make a distinction between changes in the distribution of husbands and wives by educational level and a “pure change in assortative mating” that is the consequence of a change in the degree of independence between the educational levels of husbands and wives. We present an illustration of our approach, based on data for Thailand covering the period 1985–2019. It appears that while over the whole period 1985–2019 the increase in the Theil index of non-random mating was uniquely due to a change in the educational composition of the males and females (essentially of the female population), there are several sub-periods where the “pure change in assortative mating” played an important role.