Test-retest reliability in population research

The widespread use of the questionnaire and interview as measuring instruments in population research has been, for the large part, unaccompanied by evaluation of their reliability. More than 25,000 publications in the field of population were referenced in the Population Index during the 1960s, which gives an indication of the breadth of research in this growing field. Nevertheless, virtually none of these studies addressed the problem of the reliability of the data being used. This omission is a serious one. Without assurance that responses are reliable, a researcher can never be certain that he is measuring the variable he intends to measure. In other words, validity presupposes reliability. A recent study of fertility patterns in the United States by Ryder and Westoff (1971) includes reinterview data on 382 white, married, adult women. It thus represents one attempt to assess consistency, or stability, of knowledge, attitude, and practice responses over time. The present study adds to these much needed methodological data by presenting test-retest reliability results for teenagers in a metropolitan area in the United States who completed questionnaires focused on issues related to family formation and population. The goal of this study was to ascertain if and how reliability is differentially affected by characteristics of the questionnaire and of the respondent. Specifically, it asked whether reliability varies as a function of: (1) the content (personal history, family formation, population); (2) the psychological nature of the item (knowledge; attitudes, beliefs, and opinions; desires, expectations, and intentions); and (3) the characteristics of the respondent (sex; age [younger versus older teenagers]; race [white versus nonwhite]; religion [Catholic versus non-Catholic]).