1. Accessibility of the Metropolitan Washington D.C. Public Transportation System of the Handicapped and Elderly;Abt Associates, Inc.,1972
2. A joint frequency and mode choice model for shopping trips;Adler;Transportation Research Record,1975
3. Marital status and living arrangements: March 1984;Bureau of the Census,1984
4. Marital status and living arrangements: March 1988;Bureau of the Census,1988