女性の高学歴化=少子化は本当か? ―60年ぶりの丙午の出生減から見えた新事実―

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2026-04-20 早稲田大学

早稲田大学などの研究チームは、女性の高学歴化が少子化の原因とする通説を検証し、Demographyに発表した。1966年の「丙午」による出生減を自然実験として分析した結果、教育水準の上昇は結婚や出産のタイミングをわずかに遅らせる(初婚約2週間、初産約40日)ものの、その影響は一時的で、40代半ばまでには結婚率や子ども保有率は他と同水準に収束することが判明した。つまり教育は最終的な家族形成の有無にはほぼ影響しない。高学歴女性は経済的に自立して結婚する傾向はあるが、社会的慣行は大きく変わらなかった。本研究は、少子化の主因を教育ではなく、働き方や育児環境など制度的要因に求める必要性を示している。

女性の高学歴化=少子化は本当か? ―60年ぶりの丙午の出生減から見えた新事実―
図:年齢別の教育機会をめぐる競争の緩和が家族形成に及ぼす影響(論文図4より)

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日本における教育が結婚と出生率に及ぼす因果効果:干支迷信を外生的ショックとして利用した準実験的アプローチに関する研究ノート Causal Effects of Education on Marriage and Fertility in Japan: A Research Note on a Quasi-Experimental Approach Utilizing Zodiac Superstition as an Exogenous Shock

Rong Fu;Senhu Wang;Yichen Shen;Haruko Noguchi
Demography  Published:April 01 2026
DOI:https://doi.org/10.1215/00703370-12530548

Abstract

Despite extensive research on education’s relationship with family formation, causal evidence remains limited, particularly for postsecondary education in East Asia. This research note provides novel causal evidence on education’s effects on marriage and fertility among Japanese women by exploiting a unique quasi-experimental design based on the 1966 “Firehorse” zodiac superstition. We leverage the mismatch between Japanese school year and calendar year to identify women who benefited from reduced educational competition without being directly affected by the superstition. Using a difference-in-differences approach and comprehensive data on approximately 1.8 million women from multiple administrative sources, we examine the effect of increased educational opportunities across all education levels. Our findings reveal that higher education leads to modest delays in marriage and childbearing—effects that are smaller than previously documented—without increasing lifelong singlehood. Women with more education show higher labor force participation at marriage and marry slightly younger spouses while maintaining traditional marriage practices. These results suggest that education’s direct effect on family formation is moderate and that institutional factors beyond education may deserve greater attention in understanding demographic trends in East Asia. Our findings contribute to debates about effective family policies in rapidly aging societies facing declining marriage and fertility rates.

教育
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