Features and impact of missing values in the association of self-rated health with mortality in care homes: a longitudinal study

BACKGROUND: Self-rated health (SRH) is a health measure used in studies of older adults. The objective of this study is to analyze SRH as a predictor of mortality in the institutionalized older population and the characteristics of those who do not provide information about their SRH on health questionnaires. METHODS: This is a 15-year follow-up study of older adult residents in nursing or care homes in of Madrid, Spain. SRH was measured on a 5-point Likert type scale. The association between answering the SRH question and socio-demographic and health characteristics was evaluated through prevalence ratio (PR), estimated by Poisson regression models. Survival rates associated with SRH were studied through a multivariate Cox regression. RESULTS: The sample has a mean age of 83.4 (standard deviation, SD = 7.3), with 75.7% women. Twelve percent did not answer the SRH item. Those who did not answer showed a higher probability of disability (Barthel index, PR = 0.76, 95% confidence interval = 0.67–0.86) and/or dementia (PR = 8.03, 3.38–19.03). A trend for higher mortality was observed in those persons who did not respond (adjusted hazard ratio HR = 1.26, 0.75–2.11). The mortality rate was 32% higher for those who declared poor SRH in comparison with those who reported good SRH (adjusted HR = 1.32, 1.08–1.6). CONCLUSIONS: There is an elevated number of people who do not respond to the SRH item, mainly those with disabilities and cognitive deterioration. Lack of response to SRH is a good indicator of 15-year mortality for persons institutionalized in care or nursing homes.