Dear Marie, It is very simple: 1. HUD (by USPS): A unit is vacant only after mails had not been collected for 90 days. If the mails were picked up (collected) in 30 day for example, it is not a vacant unit. 2. ACS: On survey day, a unit is treated as a vacant unit if it is not occupied. A one-day definition by ACS compares to USPS's 90-day definition. ________________________________ Richard Lin, Ph.D. Demographer Colorado Department of Local Affairs Division of Local Government 1313 Sherman Street, Room 521 Denver, CO 80203 Phone: (303)866-4989 Fax:: (303)866-2660 richard.lin(a)state.co.us www.DOLA.Colorado.Gov I compared the HUD vacancy rates with the ACS vacancy rates. The former are low and the latter very high. Have others found this too and is there an explanation? Thanks, Marie Bousfield City of Chicago _______________________________________________ ctpp-news mailing list ctpp-news(a)chrispy.net http://www.chrispy.net/mailman/listinfo/ctpp-news