eighth of the sample is included for the first time, one-eighth is in the sample for the second time, etc. The sample unit is the housing unit; if residents move over the course of the 15 months, the remaining CPS interviews are conducted with the new members of the housing unit. For this reason, the information collected may not represent panel data per se. The initial interview and the fifth interview are face-to-face interviews; the remaining interviews are conducted, if possible, by telephone. The design of the CPS implies that the FSS data are collected across mixed modes; depending on the month-in-sample, the interview may be conducted as a face-to-face or telephone interview. The respondent selected for the CPS is the person who is identified as most knowledgeable concerning the labor force status of the members of the household.

Supplements to the CPS labor force questions are included in various months; for example, in March of every year, the supplement focuses on the collection of detailed data on household income, employment, and social assistance program participation. In other months, the supplements may focus on child support payments, ownership of home computers and use of the Internet, or health-related behaviors. As noted above, the FSS is currently collected as a supplement to the CPS in December of each year. Prior to the administration of the FSS, the interviewer determines the most knowledgeable member of the household concerning food that is purchased and eaten by the household and interviews that person.

Since moving to the December field date, the rotating panel design of the CPS implies that the FSS is administered to each housing unit twice, one year apart. One caution is that, as stated above, the CPS is a housing unit–based sample; individuals and families are not followed if they move from the CPS selected housing unit. For example, a sampled housing unit for which December 2002 represented the first month-in-sample will be interviewed again in December 2003 (fifth month-in-sample). Hence, changes over a one-year interval can be examined for up to 50 percent of the sampled households that have had no change in their composition.

The reinterview of part of the sampled cases allows estimation of within-household variance for the food security measures.¹ Researchers in the Economic Research Service (ERS) of USDA are currently using the panel feature of the CPS to look at food insecurity of households as they approach the beginning of a food stamp spell, a period of one or more months during which a household receives food stamps every month. Wilde and