本篇論文使用一種新的衡量方法，也就是以雇主退休金的提撥成本，從勞工退休所得的角度，研究退休金計畫選擇的改變與退休金計畫彼此間的互補與替代關係。利用美國國稅局Form 5500 資料，本篇論文比較美國企業在1985 與1996 兩年間對退休金計畫的選擇改變。希望能提供新的研究證據，檢視401(k) 退休金計畫是否已經成為美國退休金計畫的主要選擇。另外更設計一羅吉斯回歸模型，進一步分析401(k)、確定給付退休金計畫及其他確定提撥退休金計畫三者間的互補與替代關係。研究結果發現，在主要的退休金計畫階層(Primary Plan Level)，401(k)計畫並未取代傳統的確定給付型退休金計畫，反而是取代與它性質相近的其他確定提撥型計畫；而在次要的退休金計畫階層(Secondary Plan Level)，401(k)計畫則用來補充傳統的確定給付型計畫與其他的確定提撥型計畫。 evidence of the substitution and supplementary effects between 401(k)s and other employer’s pension plans. By comparing employer’s pension plan choices in the same firm between 1985 and 1996, we trace how employers changed their pension offering from 1985 to 1996 for each individual firm. Multinomial Logit Regression Models were adopted to analyze the substitution and supplemental effects between 401(k) and other employer’s pension plans. The empirical results do not support the hypothesis that the new 401(k) offerings are used to replace existing defined benefit (DB) plans, but rather to replace existing other defined contribution (DC) plans or to supplement DB/DC plans. For the substitution effect in the primary plans, we find bigger firms and unionized firms are more reluctant to change their primary DB plans. Moreover, the change of union status did not have any influence in the changes of employer’s primary pension plan choices. For the substitution and supplemental effect in the secondary plans, we find that bigger firms, unionized firms and firms in service industry are less likely to substitute 401k plans for their existing DC plans. We also find that bigger firms and firms in service industry are more likely to supplement 401k or DC plans for their primary DB plans; whereas unionized firms and downsizing firms are more reluctant to do so.