Updating the rent sample for the CPI Housing Survey
When the 1998 Housing Survey sample was introduced in 1999, the sample had about 33,000 in-scope units. This number was far below the target sample of 50,000 units. Because of this shortfall, a sample augmentation was performed in 2000–2001 that increased the in-scope sample to about 36,000 units. This number was still short of the target.
As samples age and become out of date, they become smaller. This result is certainly true of the Housing Survey’s sample. Over time, some renter-occupied units become owner-occupied while others become nonresidential. As the burden on respondents accumulates (for some becomes excessive), more refusals occur. More importantly, because newly built rental units have no opportunity to enter the sample, the sample becomes less representative of the housing universe. For example, rent changes for newer units may be different from those of older ones. By July 2009, when the efforts to improve the sample began, the sample had approximately 16,000 fewer rental housing units than its target size. This result was due primarily to the sample shortfall in 1999, the subsequent augmentation in 2000, and the continuing sample attrition. See appendix A for details on Housing Survey sample selection.
Sample replacement and sample augmentation are ways to counteract these problems. Sample replacement drops the old sample items and brings in new ones, selected from a new, more recent sampling frame. Augmentation supplements an existing sample by adding new sample items drawn from either the original sampling frame or a new frame. An augmentation that uses a new frame requires care to assure consistency of the old and new sample observations, particularly with respect to the sample weights.
The geographic sample of the last CPI revision, which deployed in January 1998, partitioned the urban United States into 38 CPI areas and selected 87 pricing areas from the 1990 Census to represent these areas. These areas were metropolitan areas or urban places and were selected using probability proportional to size (PPS), where the size measured was the 1990 population. For the Housing Survey, the pricing areas were further partitioned into neighborhoods called segments, formed from one (in most cases) or more U.S. Census Bureau block groups and containing at least 50 housing units in large (A-size) self-representing pricing areas and at least 30 in smaller (B/C-size and D-size) non-self-representing pricing areas. With the use of PPS, a sample of segments was selected in each area, in which the size measure was the sum of renters’ actual rents and owners’ estimated implicit rents. The Census Bureau provides the number of renters, the average rents, and the number of owners by block group, whereas the BLS estimates the average owners’ implicit rents. See appendix A for details on Housing Survey sample selection. An average of about five rental housing units was selected within each segment.
New Housing Survey samples
Most of the rental units in the current (early 2012) Housing Survey entered the sample in 1999 when the CPI completely replaced the sample with a new one drawn using the 1990 Decennial Census. Some units built after the 1990 Census were included through a special new-construction survey that covered units built as recently as 2006.