Interviewer effects when investigating abuse were not compatible with effect modification but instead with confounding

Abstract

Objectives: To describe interviewer-related variability in abuse estimates and assess the nature of the interviewer effects on the associations between elder abuse and covariates. Study Design and Setting: After intensive training, six interviewers administered structured questionnaires through face-to-face interviews to assess abuse in a population-based sample of 641 Portuguese individuals aged 60–84 years. Results: The overall prevalence of abuse victimization during the previous year was 28.1%, but it differed significantly according to the interviewer, ranging from 16.9% to 36.8%. There was no statistical effect modification introduced by the interviewer on the association of abuse and its determinants. Additionally, interviewer-level variables (empathy and violence beliefs) showed no significant contribution to explain the variance attributable to potential interviewer effects. Adjusting for the interviewer had little or no effect on the odds ratio of abuse for gender, age, education, and quality of life. However, the interviewer introduced relevant confounding of the associations between abuse and other sensitive topics, such as somatic complaints. Conclusion: Although no relevant effect modification was observed, this study emphasizes the importance of the interviewer as a relevant confounder when estimating associations between sensitive variables, as it is the case of elder abuse.