本文利用Kiyotaki and Lagos (2007) 的架構，在具有在職搜尋(on-the-job search) 的勞動搜尋模型中，探討關係專屬投資 (relationship-specific investment) 的效率性。投資的效率受到兩種扭曲的影響：組合外部性 (composition externality) 及套牢問題 (holdup problem)。前者源自於工作間的異質性，而後者源自於契約的不完全 (incompleteness) 以及投資的專屬性 (specificity)。通過以解析及數值分析的方式求解模型，我們證明這兩種扭曲均可能造成投資不足 (underinvestment) 以及過度投資 (overinvestment)，而且這兩種扭曲的效果可能相互扺銷。

By adapting the model of Kiyotaki and Lagos (2007), we analyze the efficiency of relationship-specific investment in job search models that feature on-the-job search. Investment is inefficient due to two distortions: the composition externaltiy and the holdup problem. The former stems from the heterogeneity among jobs. The latter arises from the incompleteness of contracts and the specificity of investment. By solving the models analytically and numerically, we show that both distortions can lead to under- and over-investment, and that the effects of the two distortions may offset each other.