This Thomson Reuters  study funded by Sanofi Aventis and published in the Journal of Occupational and Environmental Medicine found that, even when treated with antidepressants, depressed workers exhibit substantial productivity losses.  The authors conclude that therapies to better-manage depression may provide employers additional cost-savings by increasing worker productivity. 

Curkendall et al. (2010). Productivity losses among treated depressed patients relative to healthy controls. Journal of Occupational and Environmental Medicine, 2(52): 125-130. doi: 10.1097/JOM.0b013e3181ce10a8. http://journals.lww.com/joem/Abstract/2010/02000/Productivity_Losses_Among_Treated_Depressed.2.aspx

Authors: Suellen Curkendall, Kimberly M. Ruiz, Vijay Joish, Tami L. Mark