questions (e.g., did this ever happen in the last 30 days). Therefore, in the administration of the questionnaire, the respondent is constantly being asked to shift between a 12-month and a 30-day reference period. Such shifts are cognitively difficult for respondents and should be avoided if possible.
The 12-month reporting period used in the HFSSM questions could reduce the reliability of responses. Findings from an evaluation study conducted after the 1995 survey pretest (Hess and Singer, 1995) indicated that nearly 25 percent of the respondents “failed to understand correctly the time period referred to by the question asking about ‘the last 12 months’.”
Moving to a 30-day reference period may reduce the cognitive burden of recalling phenomena for a 12-month period, but, as expected, it could also reduce the percentage of households classified as food insecure. A 30-day scale was originally developed for use in the analysis of the 1995 CPS data, but it has not been used much. Researchers at ERS have revised the scale to make it more consistent with the standard 12-month U.S. food security scale commonly used in food security household analyses. A nonlinear (Rasch model–based) scaling method was used to statistically assess both the original and revised scales (Nord, 2002b). The report of this work examines the feasibility of a 30-day food security scale, and it specifies procedures for calculating the revised 30-day scale from the FSS data and classifying households as to 30-day food security status. It also compares prevalence rates of food insecurity with hunger based on the 30-day scale with those based on the 12-month scale for the years 1998–2000. Nord found that of the 3 percent of households classified as food insecure with hunger based on a 12-month scale, 74 percent (or 2 percent of the households) were similarly classified for the 30-day period prior to the survey.5
The impact of the length of the reference period and confusion about its boundaries on the quality of the resulting data depends partly on the actual organization of the episodes of food insecurity in respondents’ lives. Both the difficulty of the reporting task and the organization of the respondents’ experiences will influence which heuristics respondents use to supplement their memory in constructing answers. For example, a respondent who experiences food shortages monthly because of the timing of income may take a monthly value and multiply by 12 to produce an answer. Another example is suggested by Bickel and colleagues (2000, p. 16), “The U.S. standard food security measure reflects the household’s situation over the 12 months before the interview…. A household that experienced food insecu-