美豬與美牛的進口法案，橫跨了我國三任不同總統執政時期，當政權轉移時，原來的反對黨成為新執政黨時，就轉為支持他們原先反對的主張；而淪為反對黨的原執政黨，在下臺後立場也似乎發生轉變。因此得到了「換了位置，就換了腦袋」的罵名。但此一說法過去僅流為坊間的討論，並未有系統的探討。在「脊迴歸」（ridge regression）與「羅吉斯迴歸模型」（logit model）的分析下，我們發現執政黨身分是一個會影響立委的法案支持強度與發言支持程度的因素，此外，初任立委與區域立委的因素也會影響立委的投票與發言行為，這樣的結果證實了「換了位置，就換了腦袋」的說法。本文不但補充了我國立法委員立場轉變的實證文獻，更補充了我國立法委員在代表取向上的研究。

In Taiwan (R.O.C.), the import bills of U.S. pork and beef have undergone the experiences of three different presidencies. Whenever an opposition party becomes the ruling party, it tends to change its posture toward the U.S. pork-beef issue, and vice versa where the previous incumbent shifts its position when it becomes the opposition. Therefore, there is an argument: where you stand depends on where you sit. However, this point needs to be confirmed through empirical evidence. In our analysis using Ridge regression and the Logit models, we ascertain that the position taken by the ruling party plays a crucial role in shaping the queries and voting behavior of legislators on the U.S. pork-beef issue. Furthermore, being first-year legislators and representing certain regions also affects their queries and voting behavior. The empirical results in this article support the argument that the position that the MPs' party is in (incumbent or opposition) influences their queries and voting intentions. Moreover, the empirical conclusion provides a new perspective on studies of changes in MPs' positions and the orientation of their representation in Taiwan (R.O.C.).