Inventive productivity in Japanese materials sector

Classical theory “Lotka´s Law” has been proven in many fields that the number of persons who contribute n outputs is about 1/n^α of those who contribute one output, where the exponent α is a parameter about 2 to 3 in the most cases reported previously. Our analysis on patent productivity of inventors in Japan shows different characteristics from the results of previous studies on US and European firms. We have studied 17 Japanese firms of materials sector and about 40,000 inventors of them who have contributed to more than 260,000 patent applications filed at the Japan Patent Office over the period 1992-2011. As a result, we find that a simple Lotka-like power law fitting is not applicable to patent distributions of the inventors in Japan. Each distribution has a turning point dividing into two domains: small patent counts with a gentle slope and large patent counts with a steep slope. This observation suggests that a typical inventor who is named as a first inventor more than once is the one who joined a firm in the R&D department and has remained there, keep involving in the inventive activities for the long year of his/her employment.