Field-of-study homogamy: Evidence from the EU

Alena Bičáková, Štěpán Jurajda 26 July 2016

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Positive assortative mating, or homogamy, is a central feature of marriage markets. Educational homogamy, the tendency to match based on one’s level of education, is particularly strong among college graduates (Schwartz and Mare 2005, Siow 2015). While the educational-level homogamy of college graduates has been well documented, the question as to whether they also match based on their field of study has so far received little attention.

If college graduates tend to match into couples within their field of study, the large differences across these fields in both earnings and in the availability of family-friendly careers could lead to sizeable consequences for household inequality and family formation. Such consequences have been extensively explored for the case of educational-level homogamy (Fernández et al 2005, Schwartz 2013, Greenwood et al 2014, Goldin 1997, Chiappori et al 2009).

Field-of-study homogamy among EU college graduates

In a recent paper, we document the extent of field-of-study homogamy (FSH) using the 2014 release of the EU Labour Force Survey (LFS), which provides information on college graduates and their marriage/cohabitation status in 24 EU countries (Bičáková and Jurajda 2016). Our cross-sectional samples consist of individuals who graduated from college between the ages of 20 and 44 and are observed from 2003 to 2013. Our analysis focuses on 128,000 married or cohabitating couples formed by two college graduates and sharing a household. These ‘college-college’ pairs represent about 80% of all couples formed by at least one college graduate. We classify a couple to be homogamous when both partners graduated from the same broad field of study – education, humanities, the social sciences, science, engineering, agriculture, health, or services.

The fact that women continue to be unevenly represented across college fields of study (Charles and Bradley 2009) implies dramatic cross-field differences in the meeting opportunities of college graduates and in the potential for FSH. In particular, the field-of-study gender supply structure has a direct, mechanical effect on the maximum extent of FSH. Consider the most ‘male’ field of study, engineering, where men represent about 80% of graduates. Most male engineering graduates will not be able to find a female partner within their field of study. On the other hand, women, who form about 20% of all engineering graduates in our data, face an abundant supply of male peers (i.e. potential partners) in their field of study. It is therefore not surprising that among the ‘college-college’ couples involving a female college graduates in engineering, 60% are homogamous. For comparison, in services, the most gender-balanced field of study, the corresponding share is only 22%.

Overall, over a third of the married/cohabiting couples formed by two college graduates in the sample are homogamous. Since it is not clear to what extent this share is driven by assortative matching on the field of study and to what extent it corresponds to the field-of-study composition of men and women (field marginal distributions by gender), we contrast the actual share of homogamous matches with a benchmark share of homogamous couples predicted under the assumption of random (independent) matching using the marginal distributions of formed matches across fields of study. We summarise the extent of FSH across the entire matching market using the ratio of the actual share of homogamous matches to the share of homogamous matches one would expect under the random matching assumption. We find that in the EU-wide sample, a randomly picked couple is almost twice as likely to be homogamous than would be predicted from matched marginals under random matching. Interestingly, the extent of FSH is almost identical among married and cohabitating couples.

However, the ‘marginal-free’ degree of positive assortative matching varies dramatically across pairs of fields of study. The extent of homogamy is lowest for the social sciences and engineering, while the maximum FSH occurs for humanities and agriculture. The pair-wise field comparisons suggest that the value of matching within one’s field of study (relative to a given mix-field alternative between the two fields) is particularly high for pairs of fields involving agriculture and is relatively low for pairs of fields involving the social sciences. While graduates in the social sciences are relatively ‘open’ to matching with graduates from other fields of study (and while science and engineering are also highly compatible), the value of matching within one’s field is very high when the alternative is a non-homogamous match between a graduate in humanities and one in agriculture. All of the odds ratios we measure for pair-wise field-of-study comparisons for couples formed by two college graduates are higher based on our data than the odds ratio corresponding to the (much explored) educational-level homogamy – that is, to matching on having a college degree or not.

Meeting in school or workplace?

Our analysis is based on country-wide groups of college graduates in the same field of study and therefore asks about the combined channels of meeting potential partners in a study program and in marriage market-wide social and workplace networks linked to one’s field of study. The average gap between partners in year of graduation is 3.4 for non-homogamous couples and only 2.6 for homogamous ‘college-college’ couples. Further, the share of homogamous couples who have graduated from college in the same year is higher, at 25%, compared to the corresponding share of non-homogamous couples, which stands at 14%. This is consistent with colleges structuring the search and matching process.

A decomposition of EU-wide trends reveals that FSH increases during the first three years after graduation and is relatively flat afterwards. Two mechanisms can underlie this pattern. First, matches effectively formed during study (in an education program or in social networks related to one’s field of study) may lead to observed (shared-household) matches only with some delay after graduation. One may expect this type of FSH gradient to plateau within a few years of graduation. Second, homogamous matches could also be initiated within workplace interactions to the extent that workplaces are segregated across fields of study (i.e. hospitals versus IT companies). The contribution of workplace interactions to FSH may be expected to grow in importance with years since graduation as the effect of social networks formed while in school fades away.

While we cannot disentangle these two mechanisms without data on the timing of initial match formation and on complete labour market histories, we can provide an initial insight into this issue by asking whether the structure of FSH is related to the couple’s industry of employment. We find that the gradient of FSH in terms of years since graduation is both more rapid and reaches higher levels for the same-industry group.  To the extent that one expects workplace interactions to gradually dominate social networks built during college studies as a source of FSH, these results are consistent with quantitatively important workplace-based matching.

Cross-country comparisons

There are large cross-country differences in the extent of FSH, with the lowest FSH in Latvia and the Netherlands and the highest in Slovakia and Greece. Countries also differ considerably in terms of gender segregation across the fields of study. This is important as the maximum potential FSH under a given marginal distribution of matches is given by the maximum number of pairs that can be formed in each field given its gender composition. A more gender-segregated composition of fields of study implies a lower potential for FSH.

We show that countries with a higher FSH potential also have a higher extent of FSH, even when measured by a marginal-free index (i.e. independent of the marginal distribution of women and men across fields of study). Further, groups of countries clearly differ in the degree to which they utilise their FSH potential – Romania, Bulgaria, Hungary, Greece, and Slovakia use more than 40% of their FSH potential. In contrast, Latvia, the Netherlands, Cyprus, Ireland, and the UK use as little as 25% of their FSH potential. Both of these groups span the entire range of FSH potential values, suggesting that varying degrees of gender segregation of field of study in college are consistent with both high and low degrees of utilisation of FSH potential and that the utilisation rates are driven by country-level structural factors (to be uncovered in future work).

Figure 1. The Gender Gap Index and FSH-potential utilisation rate (H/H(P))

Note: The Gender Gap Index, generated by the World Economic Forum, reflects economic and political opportunities, education, and well-being for women. The highest possible GGI score is 1 (equality) and the lowest possible score is 0 (inequality).

Finally, we ask whether the gender culture of a country is related to the rate at which its FSH potential is used – we plot the 2010 values of the Gender Gap Index (GGI), which reflects economic and political opportunities, education, and well-being for women, against the degree of the FSH-potential utilisation on the vertical axis.  Figure 1 reveals that higher gender equality is associated with lower utilisation of the FSH potential. The negative correlation may imply that the preference for homogamous matching is higher for college graduates in countries with more traditionally defined gender roles but the mechanism underlying this correlation should be further explored in future research.

Authors’ note: This research has been supported by the Czech Science Foundation (grant P402/12/G130). This paper was initiated while Jurajda was visiting the School of Economics at the University of Edinburgh; the School’s hospitality is most gratefully acknowledged. This research uses the 2014 release of the anonymised EU Labour Force Survey (LFS) for the reference years 2003-2013. The Eurostat has no responsibility for the results and conclusions presented in this paper.

References

Bičáková, A and Š Jurajda (2016) “Field-of-study homogamy”, CEPR Discussion Paper No. 11177.

Charles, M and K Bradley (2009) “Indulging our gendered selves? Sex segregation by field of study in 44 countries”, American Journal of Sociology, 114(4): 924–76.

Chiappori, P-A, M Iyigun and Y Weiss (2009) “Investment in schooling and the marriage market”, American Economic Review, 99(5): 1689–1713.

Fernández, R, N Guner and J Knowles (2005) “Love and money: A theoretical and empirical analysis of household sorting and inequality”, Quarterly Journal of Economics, 120(1): 273–344.

Goldin, C (1997) “Career and family: College women look to the past”, in F Blau and R Ehrenberg (eds), Gender and Family Issues in the Workplace, New York: Russell Sage Press.

Greenwood, J, N Guner, G Kocharkov and C Santos (2014) “Marry your like: Assortative mating and income inequality”, American Economic Review: Papers & Proceedings, 104(5): 348–353.

Schwartz, C R (2013) “Trends and variation in assortative mating: Causes and consequences”, Annual Review of Sociology, 39: 451–470.

Schwartz, C R and R D Mare (2005) “Trends in educational assortative marriage from 1940 to 2003”, Demography, 42(4): 621–646.

Siow, A (2015) “Testing Becker's theory of positive assortative matching”, Journal of Labor Economics, 33(2): 409–441.

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Topics:  Education Labour markets Poverty and income inequality

Tags:  Matching, assortative matching, positive assortative matching, marriage markets, graduates, homogamy, Europe, marriage

Assistant Professor, CERGE-EI

Mellon Endowment Professor, CERGE-EI

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