This study examined the effect of major depressive disorder (MDD) on work performance, as well as treatment utilization and costs to employers sponsoring health care insurance. 

Birnbaum, H. G., R. C. Kessler, et al. (2010). Employer burden of mild, moderate, and severe major depressive disorder: mental health services utilization and costs, and work performance. Depression and Anxiety, 27(1): 78-89. http://www3.interscience.wiley.com/journal/122473967/abstract?CRETRY=1&SRETRY=0 

Authors: Howard G. Birnbaum, Ronald C. Kessler, David Kelley, Rym Ben-Hamadi, Vijay N. Joish and Paul E. Greenberg