Comprises 2 types of data collections: a national survey of housing units, and surveys of housing units in selected metropolitan areas. The interviews cover core questions that are repeated each year, and an additional set of questions on recurring or one-time supplemental topics. The national data were collected annually through 1981 and have been collected every 2 years since that time. The metropolitan-area data are collected on a continuous basis and are reported annually. For the latest see the Census Bureau site.