1990 census planning : questionnaire subjects : joint hearing before the Subcommittee on Federal Services, Post Office, and Civil Service of the Committee on Governmental Affairs, United States Senate and the Subcommittee on Census and Population of the Committee on Post Office and Civil Service, House of Representatives, One Hundredth Congress, first session, May 14, 1987. (U.S. G.P.O. :, 1987)