1. Survey Research Laboratory, College of Urban Planning and Public Affairs, University of Illinois at Chicago, 412 S. Peoria St., Chicago, IL, 60607, U.S.A.
2. Medicine and Public Health, American Medical Association, 515 N. State St., Chicago, IL, 60610, U.S.A.
3. Survey Research Laboratory, University of Illinois at Chicago, 412 S. Peoria St., Chicago, IL, 60607, U.S.A.