Loss to five-year follow-up in the Telemark study

Objectives: Studies have shown that declining participation in epidemiological studies may lead to biased estimates of occurrence and selection bias. Nevertheless, studies on non-participation and loss to follow-up in prospective studies are rare. Aim: The aim of the study was to characterize those lost to follow-up and possible factors associated with non-participation in a prospective population based study of respiratory health in Norway. Methods: A five-year follow-up of the population based sample (n=16 099), aged 21-55 years, from the Telemark study was conducted in 2018. Risk factors associated with loss to follow-up were assessed by forward conditional logistic regression. Results: A total of 8 244 (51.2%) participants were lost to follow-up. Non-participation was associated with male sex, younger age, low education, current smoking, unemployment, reduced workability, asthma, being woken by chest tightness and COPD. Conclusion: The risk factors for participants lost to five-year follow-up are comparable to those reported in population-based studies for non-responders, mainly related to younger age, male gender, current smoking, low socioeconomic status, and higher symptom prevalence and morbidity.