Duncan was a consultant to President Clinton's White House Office of National Drug Control Policy during his tenure as Senior Study Director of the Substance Abuse Research Group of the Westat corporation. In his position at Westat he also provided consultation to the National Institute on Drug Abuse, Center for Substance Abuse Treatment, Center for Substance Abuse Prevention, National Academy of Science, United States Immigration and Naturalization Service, New York City Housing Authority, and SPSS Inc.. He served from 1996 to 1998 as Senior Public Health Epidemiologist in the Director's Office of the Rhode Island Department of Health where he was coordinator of health policy and Project Director of the state's Unified Needs Assessment Program for Substance Abuse Prevention and Treatment.