【摘要】 中国企业职工基本养老保险基金的收入规模持续增加，同时低收入群体的缴费意愿却下滑较为明显，鲜有文献从基数调整的视角提供相关的理论解释和因果证据。本文基于应税收入弹性理论的经典框架，利用中国城镇住户调查月度数据和基数调整的月份差异构造双重差分模型，试图对中国企业职工基本养老保险基金增收的微观机制与适应策略展开研究。结果发现，提高养老保险缴费基数下限使基金收入总体上增加约2.55%，这主要源于基数申报标准的提高（机制效应），但同时也会降低下限遵从概率（行为效应），两种效应的具体表现与职工年龄、技能水平和缴费压力等个体特征紧密相关。进一步的缴费分担研究表明，基数下限调整引致的缴费增加主要由低收入群体承担，并促使企业采取“低增高减”的基数申报策略。反事实估计发现，通过实施不同类型的做实缴费基数政策，可以进一步将提高基数下限的基金促收效应提升到样本均值的10.98%—59.80%。为了缓解做实缴费基数可能引发的负向效应，地方政府可以通过完善缴费基数政策、调整单位费率和强化征管统筹等策略进行积极应对。研究结论对“十五五”时期健全社会保障基金长效筹集机制，促进社会保障事业高质量发展具有重要的政策意义。更多还原

【Abstract】 The contribution of pension funds for enterprise employees continues to grow, but the quality of fund financing has declined. The willingness to contribute among low-income groups has notably decreased, which has drawn widespread public attention. Previous studies have shown that contribution parameters are pivotal to the revenue size and financing quality, with high contribution rates and weak enforcement as the key drivers of low compliance. Nevertheless, changes in contribution rates and enforcement cannot explain the paradox of rising revenue alongside declining financing quality, nor can they account for the differential changes in enrollment behaviors across different groups. In contrast, the continuous rise of the contribution base, particularly the increase in its lower limit, directly raises the contribution burden on low-income employees and may exert a suppressive effect on their enrollment behaviors. From this perspective, contribution base adjustments may offer a more critical analytical lens to explain the above phenomena. Regrettably, there is a scarcity of literature providing relevant theoretical explanatory frameworks and causal empirical evidence.Based on the classic theoretical framework of the elasticity of taxable income with respect to marginaltax rates, this paper constructs a difference-in-differences model by utilizing the monthly data from the Urban Household Survey and the differences in the months of contribution base adjustments to study the micro mechanisms and adaptation strategies of China’s increasing pension funds for enterprise employees. We find that raising the lower limit of the contribution base for pension insurance generally increased the fund income by approximately 2.55%, mainly due to the elevation of the contribution base reporting standard(mechanism effect), and at the same time, it would also reduce the probability of compliance with the lower limit(behavioral effect). The specific effect type and its magnitude are closely related to individual characteristics, such as age, skill level, and contribution pressure. Further analysis on contribution distribution indicates that the increase in fund incomes resulting from contribution base adjustments is mainly borne by low-income groups and prompts enterprises to adopt astrategy of increasing the contribution base for low-income groups and underreporting the contribution base for high-income groups. Through counterfactual estimation, it is found that implementing different types of policies to solidify the contribution base can further enhance the fund’s income-boosting effect of contribution base adjustments to 10.98%–59.80%. To alleviate the negative effects that may arise from solidifying the contribution base, local governments can take proactive measures such as improving the contribution base policy, adjusting the contribution rates, and strengthening tax enforcement.This paper makes three main marginal contributions to the literature. First, it applies the analytical framework of the elasticity of taxable income with respect to marginal tax rates to the context of China’s social security contribution system, ingeniously identifying the theoretical relationship between contribution base adjustments and pension funds for enterprise employees and their mechanisms. Second, this study leverages the exogenous variations in the timing of contribution base adjustments across regions, and innovatively addresses the causal identification problem related to contribution base adjustments, thereby bridging a critical gap in the understanding of automatic indexing policies. Third, it provides the first microempirical evidence of enterprises’ reporting behaviors of the contribution base, offering a new perspective for understanding the widespread underreporting of the contribution base in China.更多还原