本文使用二〇〇四年至二〇二四年的戶籍行政資料與所得稅資料，觀察祖父母在第一位孫子女出生前後的薪資所得與就業變化。實證方法包括個人固定效果模型與事件研究法，並進一步以第一胎子女性別作為工具變數，建構工具變數事件研究模型，以處理孫子女出生時點可能存在的內生性問題。

研究結果顯示，第一位孫子女出生後，祖父與祖母的所得及就業均持續下降，顯示成為祖父母與其中高齡階段的勞動市場連結減弱有關。祖父與祖母的所得下降軌跡大致相似，但就業結果呈現明顯的性別差異，祖母的就業下降較早出現，且幅度明顯大於祖父。此一結果顯示，祖母較可能透過退出受僱就業或降低勞動市場參與進行調整。工具變數事件研究的估計結果與基準事件研究大致一致，顯示主要發現並非完全由孫子女出生時點的內生性所驅動。異質性分析顯示，父系祖父母、較年長世代，以及與孫子女居住於同一縣市的祖母，其勞動供給反應較為明顯。這些結果與家庭照顧責任仍較集中於女性，以及地理距離與傳統家庭規範可能影響代間照顧安排的解釋一致。

本研究顯示，中高齡者的勞動供給決策會受到孫子女出生伴隨而來的家庭照顧責任影響。政府在推動延後退休與中高齡就業政策時，也應同步提供完善的家庭照顧支持措施，以降低祖父母因照顧孫子女而退出勞動市場的可能性。

This study uses administrative household registration and income tax records from 2004 to 2024 to examine changes in grandparents' wage earnings and employment around the birth of their first grandchild. The empirical analysis employs individual fixed-effects models and an event study design. To address potential endogeneity in the timing of grandchild birth, we further implement an instrumental-variable event study design.

The results show persistent declines in both earnings and employment among grandfathers and grandmothers following the birth of their first grandchild, suggesting that the transition into grandparenthood is associated with weaker labor-market attachment in middle and older age. The earnings trajectories of grandfathers and grandmothers are broadly similar, whereas the employment results reveal a pronounced gender difference. This pattern suggests that grandmothers are more likely to adjust by exiting wage employment or reducing their labor-market participation. The instrumental-variable event study estimates are broadly consistent with the OLS estimates, indicating that the main findings are not driven solely by endogenous timing of grandchild birth.

This study shows that the labor-supply decisions of middle-aged and older individuals are affected by the family caregiving responsibilities associated with the birth of a grandchild. When promoting delayed retirement among middle-aged and older workers, the government should also provide comprehensive support for family caregiving to reduce the likelihood that grandparents withdraw from the labor market to care for their grandchildren.

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