本文利用美國職棒大聯盟1997年到2005年9個球季，156位自由球員的樣本資料，檢定大聯盟球員在出走年的表現是否較出色的問題。文中先介紹美國職棒的歷史背景與制度演進，接著探討棒球統計數據的選擇，進而運用WARP1 (Wins Above Replacement Player, level 1) 的數據作統計檢定。這個數據評估每一年每一個球員綜合投、打、守三個部份的成績幫他的球隊多贏了幾場球，也就是把球員的各項攻守數據整合成單一的一個數字，來看球員對球隊勝場數的貢獻。

WARP1的敘述統計資料呈現球員在出走年的表現的確比出走年前後來得出色，進行統計推論的結果也傾向支持這個論點。對此檢定結果，本文也嘗試以經濟學的觀點出發，探討資方在自由球員市場上的行為背後隱含的因素及球員在球團經營中所扮演的角色。

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