Ronald C. Kessler, Patricia A. Berglund, Catherine Coulouvrat, Goeran Hajak, Thomas Roth, Victoria Shahly, Alicia C. Shillington, Judith J. Stephenson, and James K. Walsh, «Insomnia and the Performance of US Workers: Results from the America Insomnia Survey,» SLEEP 34 (2011): 1161–71.