過去有許多文獻在探討市場競爭對於公司投資決策的影響，然而多數使用如靜態指標或競爭結果如市場集中度(HHI)捕捉市場競爭程度，本研究採用Hoberg, Phillips and Prabhala (2014)建構之產品組成變動做為市場競爭指標，產品組成變動是衡量公司產品在相關領域與同業產品組合變動的文本相似度，產品組成變動可視為公司主動對市場競爭的反應，較具前瞻性。，本文探討產品組成變動對於公司投資及投資效率的影響，實證結果顯示，當公司過去過度投資時，產品組成變動與投資正相關、與投資效率負相關；當公司過去投資不足時，產品組成變動與投資正相關、與投資效率亦為正相關。進一步的分析發現上述效果會隨著產品組成變動上升而遞減，且高現金部位的公司即使過去是過度投資公司，產品競爭程度上升時增加投資會使投資效率上升，與以往文獻一致。
;Prior studies on how market competition affects corporate investment policies mostly utilize measures which capture the results of the competition e.g. Herfindahl-Hirschman Index (HHI). I utilize Hoberg, Phillips and Prabhala (2014) product market fluidity, a text-based measure on the relation between the firm’s product mix and the change of whole product market. Such a measure captures the firm’s direct reaction of the market competition, thus is a forward- looking measure of market competition. In this paper, I examine the effect of product market fluidity on the company investment policy and investment efficiency. The empirical results show that product market fluidity has a positive impact on investment and a negative impact on investment efficiency on overinvestment firms. On the other hand, product market fluidity has a positive impact on investment and investment efficiency on underinvestment firms. Further analyses show that product market fluidity’s effect on investment and investment efficiency are presented among high cash-holding and overinvestment firms.