除勞動、資本等內部管理投入外，外在環境也會影響廠商的生產績效。由於外在環境的影響有其重要的政策涵義，因此如何將外在環境對績效的影響抽離出來，以獲得純管理層面的生產力，則為晚近生產力研究者所關注。囿於資料的限制，本文選取四個外在環境變數（即公路密度、工業用土地面積、高中以上程度人數、環保稽查人數），並用Malmoquist生產力指數，衡量比較民國七十三年至八十年與八十年至八十五年間，臺灣各縣市製造業中小企業在摒除外在環境影響後之生產力的變化情況，實證結果發現：在此期間內，各縣市產業之間確實出現競爭優勢互異的現象。

Besides the internal controllable factors such as labor and capital, the external environment could influence the ability of the firm to transform inputs into outputs. Because the effects of the external environment on firm’s performance has important policy implications, the recent researchers concern how to measure managerial productivity by incorporating the exogenous environment characteristics. Being subject to the data availability, the paper only includes four external environment variables (i.e. highway density, lands available for industrial use, population with senior high school and above, and the official employees for environment protection). Productivity change of small and medium-sized Taiwan manufacturing enterprises under incorporating the influence of external environment variables are measured and compared under incorporating the influence of external environment variables are measured and compared by the Malmquist productivity index at prefectures and cities level among the two periods of 1986~1991 and 1991~1996. the main empirical result is the firms of prefectures and cities show the phenomenon of rising or falling in competitiveness among most industries in above periods.