Gorton, Gary, and Frank Schmid. "Class Struggle Inside the Firm: A Study of German Codetermination." Working Paper, Wharton School Center for Financial Institutions, University of Pennsylvania, August 2000.

Finds that returns on assets and price/book ratio were lower for German firms where employees had a relatively higher degree of influence in management of the firm during the 1989-1993 time period. This is a very large and carefully-prepared study, which can be downloaded from:

http://fic.wharton.upenn.edu/fic/papers/00/0036.pdf