摘要：The aim of this paper is to empirically evaluate the "scale effect".as in Segerstrom (1998). To this end, we firstly build a new concordance table between SIC and USPCS codes. Then we analyze the difficulty index of each U.S. manufacturing industry using the patents forward citations data. Finally we evaluate by SUR method the relation between the difficulty index and the number of S&E by industry. Our investigation concludes showing that in the traditional sectors the "scale effect".is lower than in the new ones
