出生率内生型世代重複モデルによる年金財政方式の比較分析

島澤, 諭

doi:10.51094/jxiv.3479

##article.authors##

島澤, 諭関東学院大学経済学部

DOI:

https://doi.org/10.51094/jxiv.3479

キーワード:

出生率内生化、 OLGモデル、出生率連動型社会保障

抄録

少子高齢化と年金財政の持続可能性の低下が同時進行する現代において、両者の連関を規定する年金財政方式の選択は重要な政策課題である。本稿は、積立方式（FF）・賦課方式（PAYG）・給付連動型（3a）・保険料減免型（3b）の四制度がもたらす勤労期の負担構造の差異が、出生率および資本蓄積を通じて財政持続性に与える長期的影響を、出生率内生型OLG一般均衡モデルにより理論的に分析する。

本稿では、出生率連動型年金制度（3a・3b）が、PAYGおよびFFが生じさせる現役期の資源制約の歪みをどの程度・いかなる経路で緩和できるかを、子ども数の限界費用・限界便益への分解により評価する。給付連動型（3a）は老後扶養外部性を将来便益の増大を通じて内部化するのに対し、保険料減免型（3b）は現役期の育児限界費用を即時に削減する。この作用経路の非対称性が、割引因子と利子率の閉じた関数として表現される（3b）の優位条件をもたらすことを命題として導出する。あわせてFF固有の強制貯蓄による出生抑制経路を定式化し、負担・出生・資本蓄積・財政持続性を結ぶ動学的フィードバックの安定性を制度別に確立する。

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