Population Density, Fertility, and Childcare Services from the Perspective of a Two-Region Overlapping Generations Model

少子化問題に直面している日本をはじめとする国々では、人口密度の高い地域ほど、低い出生率となる傾向が確認されるが、抜本的な育児支援政策を実施することで人口密度の高い地域でも育児と仕事の両立が可能となることを通じて出生率を引き上げ、もって地域間の出生率格差を縮めることが可能か否かという考察を深めることは、重要な分析テーマである。

そこで、本稿では、人口移動や地価を組み込んだ2地域OLGの簡単な理論モデルを構築し、人口密度や保育サービスが出生率に及ぼす影響を分析している。その結果、明らかとなることは以下の3点である。

第1は、人口密度の増加に伴う混雑コストが存在する場合、各地域の人口密度が高まると、その地域の出生率は低下するが、当該地域の保育サービス水準を引き上げることで育児の時間的コストを低下させると、人口密度の増加が出生率に及ぼす影響を低減させることができることである。

第2は、人口規模が生産性に及ぼす効果が一定値未満のとき、保育サービス水準の引き上げは人口密度の相対比率を高める方向に働くが、人口規模が生産性に及ぼす効果が一定値を超えるとき、保育サービス改革で育児の時間コストの相対比率が低下すると、人口密度の相対比率は低下することである。

第3は、各地域が自らの地域居住者に賃金税を課し、その税収を財源として自らの地域に保育サービスを供給する分権戦略を取る場合、各地域における代表的個人の効用を最大にする保育サービス水準は他地域の保育サービス水準に依存せず、当該保育サービス水準は支配戦略となることである。

In countries confronting the issue of low fertility such as Japan, dual trends showing higher regional population density associated with lower fertility rates are being confirmed. It is therefore an important theme for analysis to deepen discussions related to reducing regional fertility disparities by increasing fertility through the implementation of comprehensive childcare support policies, which might facilitate the striking of a balance between child-rearing and work, even in highly populated regions.

As described herein, we constructed a simple theoretical two-region overlapping generations (OLG) by incorporating migration and land prices. Using it, we analyzed the effects of population density and childcare services on fertility. Results elucidated the following three points.

First, in the presence of congestion costs associated with increased population density, the fertility rate of the region decreases with increased population density. However, if the time cost of child-rearing is brought down by raising the level of the childcare services provided in the region, then the effect of increased population density on fertility can be restrained.

Second, when the effect of population size on productivity is less than a certain level, improvement in the childcare services raises the relative ratio of the population density. When the effect of population size on productivity exceeds a certain level, however, the relative ratio of the population density decreases if the relative ratio of the time cost of child-rearing decreases as a result of childcare service reform.

Third, where each region imposes a payroll tax on its residents and uses its tax revenue as the financial resources to adopt a decentralized strategy of providing childcare services to its region, the level of childcare services that maximizes the utility of a representative agent in each region is independent of the childcare services of any other region. Therefore, manipulation of the level of childcare services becomes a dominant strategy.

Published: Ishida, Ryo, Kazumasa Oguro, and Masaya Yasuoka, 2018. "Population density, fertility, and childcare services from the perspective of a two-region overlapping generations model," Economic Analysis and Policy, Vol. 59, pp. 29-39
https://www.sciencedirect.com/science/article/pii/S0313592617300930