Attrition in a population-based cohort eight years after baseline interview: The Cornella Health Interview Survey Follow-up (CHIS.FU) Study

Purpose To examine how response at follow-up varied from baseline sociodemographic data in a Spanish population-based cohort after 8 years of follow-up. Methods The Cornella Health Interview Survey Follow-up (CHIS.FU) Study is a population-based cohort study on lifestyle risk factors and their consequences on health status with 2500 participants at baseline. We have compared the distribution of baseline characteristics according to the results at follow-up (interview, decease, migration, or refusal). Results Almost two-thirds of the subjects who did not respond to the follow-up interview had died or moved to another town. Sex was a determinant of attrition in deceased and non-traced participants. Refusal appeared to be associated with working status and place of birth. Self-perceived health was one of the characteristics associated with mortality; subjects who perceived their health as poor were 2.6 times more likely to die than those who felt they were in good health. Disabled and retired subjects together with housewives showed a higher risk of dying than individuals still working. The determinants of attrition among emigrated subjects were civil status, age, level of studies, working status, and birth place. Conclusion Although the attrition was non-random, there was no serious bias in estimates of change and in determinants of change due to attrition.