1. Institute for Social Research; University of Michigan; Ann Arbor Michigan USA
2. Department of Biostatistics and Computational Biology; University of Rochester; Rochester New York USA
3. Department of Statistics; University of Michigan; Ann Arbor Michigan USA
4. Treatment Research Center and Center for Studies of Addictions, Department of Psychiatry; University of Pennsylvania; Philadelphia Pennsylvania USA
5. Center on the Continuum of Care in the Addictions, Department of Psychiatry and Philadelphia Veterans Administration Medical Center; University of Pennsylvania; Philadelphia Pennsylvania USA
6. VISN 4 MIRECC, Cpl Michael J Crescenz VA Medical Center and the Department of Psychiatry; University of Pennsylvania; Philadelphia PA USA