日本における学歴結合・婚前妊娠が出生力格差に与える影響
Educational Assortative Mating, Bridal Pregnancy, and Childbearing inContemporary Japan
打越文弥（東京大学・院），茂木良平（バルセロナ自治大学・院）
Fumiya Uchikoshi (Univ. of Tokyo), Ryohei Mogi (Universitat Autónoma de Barcelona)ucks@l.u-tokyo.ac.jp
Introduction
This study examines the impact of educational assortative mating on fertility
outcomes in contemporary Japan. Previous studies argued that the relative
improvement of women's better access to higher education accompanies an increase in
the number of women having stable jobs and marrying a partner whose socioeconomic
status is same or lower than themselves. However, little is known about theconsequence of “the end of hypergamy” (van Bavel 2012) on demographic outcomes.
Nomes and van Bavel (2016) provided three causal paths to hypothesize thathypogamic unions are negatively associated with fertility. First, opportunity cost ofchildbearing could be considerably high in households where women outearn theirhusbands. Second, there are differentials in marital timing between the lower andhigher educated. Third, women’s preference towards the number of children might beassociated with expected spouse pairings. Women who want to have more children
might project to rely on husband’s earning potential, while highly educated women
without preference for childbearing selectively choose partners whose status are lower
than themselves. Therefore, women of hypogamic unions are assumed to have fewer
children compared with wives of other types of assortative mating.
In the Japanese context, however, an alternative hypothesis could beproposed. In Japan, a relative increase in bridal pregnancy (BP hereafter) has been
paid attention in demography. Related to assortative mating, Raymo and Iwasawa(2008) argued BP is associated with the likelihood of non-normative unions (i.ehypogamy). To add, if this type of marriage is really ‘unexpected’, as the marriage
preceded by pregnancy is associated with lower marital quality (Teachman 2002), it ispossible to assume that this unexpected and non-normative union would not produce
additional childbirth. Therefore, this hypothesis predicts that hypogamy is positively
associated only with the first childbirth, which is mediated by its linkage to BP.
Data and Methods
Based on the research interest, this study examines the relationship between
educational assortative mating and fertility outcomes possibly mediated by BP in
Japan using Japanese General Social Survey Life Course Study (JGSS-LCS 2009),
which allows us to capture the detailed information of respondent’s demographic

events and occupational careers at month level. We estimate the hazards by parity
using discrete time event history model. The total sample used for the analysis is 1225
Japanese female aged 28 to 42 in 2008 who experienced marriage.
Results and Discussion
Table 1 shows a result of the analysis. For the 1st childbirth, model 1 showshypogamic unions in which respondents are not university graduates are more likely
to have their 1st child than other types of couples. However, model 2, which omits casesof BP, indicates that this relationship is partly explained by the likelihood of
hypogamic unions to experience BP. As we assumed, hypogamy does not affect 2nd and3rd childbirth. However, model 3 and 4 suggest that BP at 1st childbirth is positively
associated with additional child bearing but the effect is decreased and not statisticallysignificant after controlling age at first childbirth, while model 5 and 6 present BPstrongly predicts 3rd childbirth in spite of controlling the age at 2nd childbirth. We will
discuss implications of these results and provide future perspectives.
Table 1. Results of Discrete Time Event History Model by Parity

Time at risk
Couple's pairing (ref: hypogamy)
Homogamy

1st Childbirth
Model 1Model 2

2nd Childbirth
Model 3Model 4

3rd Childbirth
Model 5Model 6-0.011***0.000-0.005***0.000-0.006***0.000-0.009***0.000-0.011***0.000-0.007***0.000-0.084-0.1870.056

0.010-0.114-0.264Hypergamy
Both partners high educated-0.328***-0.366***-0.247**-0.198*-0.069-0.028-0.0530.026-0.193-0.156-0.256-0.134

Hypogamy (univ. educated women)-0.512***-0.519**Bridal pregnancy
Age at the last child birth-0.215-0.147-1.050-0.8960.173**

0.076-0.040***0.569***

0.397***-0.084***

Constant
Observations-2.994***32531-3.350***31217-3.887***36513-2.747***36513-4.990***41027-2.324***41027

Log Likelihood-4116.449-3360.394-3400.705-3394.681-1329.781-1323.216

Pseudo R2
0.015
0.006
0.006
0.008
0.018
Source: JGSS-2009, * p<0.1 ** p<0.05 *** p<0.01 (all models include birth cohort as a control variable)

0.023

Acknowledgment
The Japanese General Social Survey 2009 Life Course Study (JGSS-2009LCS) is designed andcarried out by the JGSS Research Center at Osaka University of Commerce (Joint Usage/ResearchCenter for Japanese General Social Surveys accredited by MEXT).

References
Nomes, E. and J. Van Bavel. 2016. “Marital Fertility and Educational Assortative Mating Before,
During and After the Baby Boom in Belgium.” paper presented at the IUSSP Seminar on Linking

Past to Present, Kashiwa, December 9-10.
Raymo, J. M. and M. Iwasawa. 2008. “Bridal Pregnancy and Spouse Pairing Patterns in Japan.”

Journal of Marriage and Family 70(4):847–60.
Teachman, J. D. 2002. “Stability Across Cohorts in Divorce Risk Factors.” Demography 39(2):331–51.
Van Bavel, J. 2012. “The Reversal of the Gender Gap in Education and Female Breadwinners inEurope” Vienna Yearbook of Population Research 10:127–54.