Loss to 5-year follow-up in the population-based Telemark Study: risk factors and potential for bias

• Published in: BMJ open 2023-03, Vol.13 (3), p.e064311-e064311
• Main Authors: Zivadinovic, Nikola, Abrahamsen, Regine, Pesonen, Maiju, Wagstaff, Anthony, Torén, Kjell, Henneberger, Paul K, Kongerud, Johny, Fell, Anne Kristin Moeller
• Format: Article
• Language: English
• Subjects: Asthma; Asthma - epidemiology; Bias; Chronic obstructive pulmonary disease; Clinical Medicine; EPIDEMIOLOGY; Follow-Up Studies; Gases - adverse effects; Gender; Humans; Klinisk medicin; Lung diseases; Male; Molecular weight; OCCUPATIONAL & INDUSTRIAL MEDICINE; Occupational Exposure - adverse effects; Occupations; Population; Population-based studies; Prospective Studies; Pulmonary Disease, Chronic Obstructive - epidemiology; Questionnaires; RESPIRATORY MEDICINE (see Thoracic Medicine); Response rates; Risk Factors; Socioeconomic factors
• ISSN: 2044-6055; 2044-6055
• DOI: 10.1136/bmjopen-2022-064311

ObjectivesThis study aimed to characterise participants lost to follow-up and identify possible factors associated with non-participation in a prospective population-based study of respiratory health in Norway. We also aimed to analyse the impact of potentially biased risk estimates associated with a high proportion of non-responders.DesignProspective 5-year follow-up study.SettingRandomly selected inhabitants from the general population of Telemark County in south-eastern Norway were invited to fill in a postal questionnaire in 2013. Responders in 2013 were followed-up in 2018.Participants16 099 participants aged 16–50 years completed the baseline study. 7958 responded at the 5-year follow-up, while 7723 did not.Main outcome measuresχ2 test was performed to compare demographic and respiratory health-related characteristics between those who participated in 2018 and those who were lost to follow-up. Adjusted multivariable logistic regression models were used to assess the relationship between loss to follow-up, background variables, respiratory symptoms, occupational exposure and interactions, and to analyse whether loss to follow-up leads to biased risk estimates.Results7723 (49%) participants were lost to follow-up. Loss to follow-up was significantly higher for male participants, those in the youngest age group (16–30 years), those in lowest education level category and among current smokers (all p