Survey methodology is applied regularly in medical, nursing or social science studies examining elderly populations. Research in nursing home residents, where age-related or pathological declines in cognitive function are highly prevalent, faces several methodological challenges. The quality of survey data may be subject to population-specific measurement errors. In this article, data of two studies about pain in nursing homes are used to examine which respondent-, survey- and item characteristics predict item nonresponse. Chances for non-substantial answers are higher for older residents, for females and for those with more cognitive impairment. If residents are in pain, valid answers are more likely. …