Interviewer effects in a survey examining pain intensity and pain interference in nursing home residents

Introduction Face-to-face surveys are applied frequently when conducting research in older populations. Interviewers play a decisive role in data quality, may affect measurement and influence results. This study uses survey data about pain in nursing home residents and analyses, whether affiliation-of-interviewer (internal vs. external to nursing home) and gender-of-interviewer affect residents' responses in terms of interviewer variance and systematically varying pain reports. Methods Overall, 258 nursing home residents with up to moderate cognitive impairment were examined by 61 interviewers about pain intensity and interference applying the Brief Pain Inventory. Interviewer variance was measured using intra-interviewer correlation coefficients (rho). Two-factorial covariance analysis was applied to analyse whether pain intensity and interference scores differ by interviewer characteristics. Results Interviewer heterogeneity accounts for almost one quarter of total variance on average. Interviewer variance is higher for internal and male interviewers than for external and female interviewers. Covariance analyses show significant effects of interviewer characteristics on pain reports. Average pain intensity and interference scores vary considerably by interviewer gender and affiliation. Highest pain intensity was reported towards female internal and male external interviewers; highest pain interference was reported towards male external interviewers. Conclusion Residents' answers substantially differ in relation to who is assessing pain. There is a risk of imprecise and biased survey estimates on sensitive topics like pain in nursing homes. Interviewer gender and affiliation seem to evoke gender-specific and status-related expectations and attributions which influence residents' response process. Interviewer effects pose a considerable threat to survey data quality in institutionalised older populations.