本文研究當開放型共同基金之成長與其過去績效呈正相關時，所可能引發的代理問題。基金成長與績效的關係可視為基金經理人與投資人之間的一個隱含契約。此一隱含契約將使基金之管理費用不僅與當期之基金績效有關，而且與其前期績效有關。如果成長與績效的關係包含了競賽性報償制度，基金之管理費用將具有買權的性質。因此對於基金經理人而言，本期之最適基金風險會與其前期績效有關。一般而言，一個過去績效優良的經理人會採用保守的投資策略；而績效不良的經理人會採用激進的投資策略。

This paper examines the potential agency problems in the portfolio mnage-ment when an open-ended fund's growth is positively related to its past performance. The dependence between a fund's performance and its growth creates creates an implicit contract in which the management fee is affected not only by a manager's performance in the current period but also by his prior performance. In particular, a tournament reward struc-ture will create performance bonuses in the management fee function. Ex ante, the bonus is similar to a call option on the fund's portfolio. We show that the optimal portfolio risk level in the second period depends on how the manager's performance in the first period has affected the value of bonuses in the management fee. In general, a manager with good past performance will become conservative, while a manager with poor past performance will become aggressive. Simulations are also performed to examine the robustness of the model.