Three studies-the National Immunization Survey (NIS), National Household Education Survey (NHES), and American Housing Survey (AHS)-are not good candidates for enhancement because they use sample designs and/or data collection methods that are likely to exclude current and recently homeless families, as well as families that are currently residentially unstable. The NIS and NHES surveys use random-digit dialing (RDD) to identify study participants. Random digit dialing involves selecting telephone numbers at random from a frame of all possible telephone numbers. While RDD is a reliable and efficient method for randomly selecting a national sample, unless a currently homeless person or family happens to have a cell phone, RDD will exclude people and families who are currently living on the streets and/or in shelters. It is also likely to undersample those who are precariously housed, since they are likely to be part of the small percentage of households that do not have a phone or have phone numbers that are routinely disconnected.
In addition to these problems with their sampling frames, the NIS and NHES use computer-assisted telephone surveys (CATI) to collect data. Reliance on the telephone to collect data is further likely to lead to an underreporting of both current and recently homeless people and families. The AHS uses an area probability sample to identify study participants. In this approach, the country is broken down into various geographic units, with the smallest often having only 100 to 200 housing units (e.g., street addresses), and various methods are then used to randomly select these small geographic units or segments. Area probability samples have a better chance of including homeless families in their data sample, however, when they include group quarters, such as homeless shelters and transitional housing, in their sample frame. Unfortunately, the AHS excludes group quarters from its sample design. Furthermore, the AHS design of interviewing households living at the same address initially selected (e.g., returning to 100 Main Street each time), even if the household living there has changed since the previous survey, minimizes the likelihood of identifying homeless and at-risk families.