Abstract
Extant theory and empirical evidence suggest that strategies of diversification and geographic scope expansion carry benefits as well as costs. However, it is unclear whether the arguments relating diversification and geographic scope expansion with firm performance are applicable in the specific context of professional service firms (PSFs). These firms are also characterized by particular organizational features, such as the importance of maintaining an optimal leverage ratio, defined as the ratio between junior professionals and senior ones as partners. Our hypothesis development suggests an inverted U-shaped relationship between service line diversification, geographic scope and leverage on the one hand, and PSF performance on the other. We empirically test these relationships using fixed-effects regression and polynomial response surface analysis (RSA) on panel data from 61 German law firms from 2003 to 2012. RSA provides a finely-grained understanding of the relationships among the variables of interest. We find an inverted U-shaped performance effect of diversification and leverage, but no relationship between geographic scope and performance. Moreover, we find evidence of a complementary relationship between diversification and leverage ratio. We conclude with a discussion of our findings and their implications for theory and practice.