Reproducibility of Responses to Telephone Interviews: Demographic Predictors of Discordance in Risk Factor Status

Abstract

The reproducibility of responses to the Behavioral Risk Factor Surveillance System questionnaire was examined across the demographic strata used by the Centers for Disease Control and Prevention and state health departments for reporting prevalence estimates (specifically age, sex, income, employment, and marital status), as well as race/ethnicity, which has been previously examined. The authors administered the questionnaire twice, 21-94 days apart, to randomly selected residents of Massachusetts (response rates: first administration, 68% of eligible households; second administration, 68% of persons who completed the first interview). Initial interviews were conducted in March and October 1992. Among 448 respondents to both interviews, group mean distributions of seven demographic characteristics and 19 risk factors were highly consistent across the two interviews. Discordance in individual risk factor status ranged from 1.2% to 21.8% (median, 7.8%) and was symmetric in direction, i.e., as many respondents were considered at increased risk on the basis of the first interview and at low risk on the basis of the second interview as the reverse. Kappas ranged from 0.30 to 0.90 (median, 0.75). Education, household income, and interval between administrations were not associated with prevalence of discordance for any risk factor. Sex, age, race/ethnicity, marital status, and employment status were each predictive of variation in discordance for one or more risk factors, but no consistent effect of any individual demographic characteristic across risk factors was observed. The questionnaire has relatively uniform and generally good reproducibility across all demographic strata used for monitoring the Health Objectives for Year 2000 and other chronic disease surveillance activities.

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“…Good reproducibility ensures that temporal variations in these indicators refl ect actual variations in behavior among the population, rather than indicator instability. 2,12 Indicator validity, i.e., in the present scenario, the ability of indicators obtained by VIGITEL to provide results that are similar to those obtained by three 24-hour recalls, was also evaluated from both collective and individual perspectives. On the collective level, the telephone interview revealed a frequency of "inactive in four domains" quite similar to that obtained by the 24-hour recalls (22.5 and 19.8%, respectively).…”

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“…First, diabetes status was selfreported and, in the absence of a clinical patient history, some individuals in the sample might not have had diabetes and would thus be expected to have A1C levels near normal. However, previous studies have suggested that the self-reported diabetes variable has high reproducibility and validity (14,15), and there is little reason to believe that errors in self-reporting would increase over time. Second, although respondents reported time since diagnosis of diabetes, information on diabetes onset is not available.…”