Article Text
Abstract
Objectives Selective participation can bias results in epidemiological surveys. The importance of health status is often suggested as a possible explanation for non-participation but few empirical studies exist. In a population-based study, explicitly focused on sickness absence, health and work, we examined whether a history of high levels of sickness absence was associated with non-participation.
Design The study is based on data from official sickness absence registers from participants, non-participants and the total target population of the baseline survey of the Health Assets Project (HAP).
Setting HAP is a population-based cohort study in the Västra Götaland region in South Western Sweden.
Participants HAP included a random population cohort (n=7984) and 2 cohorts with recent sickness absence (employees (n=6140) and non-employees (n=990)), extracted from the same overall general working-age population.
Primary outcome measures We examined differences in participation rates between cohorts (2008), and differences in previous sickness absence (2001–2008) between participants (individual-level data) and non-participants or the target population (group-level data) within cohorts.
Results Participants had statistically significant less registered sickness absence in the past than non-participants and the target population for some, but not all, of the years analysed. Yet these differences were not of substantial size. Other factors than sickness absence were more important in explaining differences in participation, whereby participants were more likely to be women, older, born in Nordic countries, married and have higher incomes than non-participants.
Conclusions Although specifically addressing sickness absence, having such experience did not add any substantial layer to selective participation in the present survey. Detailed measures are needed to gain a better understanding for health selection in health-related surveys such as those addressing sickness absence, for instance in order to discriminate between selection due to ability or motivation for participation.
- Selection bias
- Sickness absence
- participation rate
- survey
- EPIDEMIOLOGY
This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
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Footnotes
Contributors MK, JL, GH, SØ and KH designed the study. MK analysed the data and wrote the first draft and main revisions of the manuscript. All authors contributed in interpretation of the data and critical revision of the manuscript, and approved the final version of the manuscript.
Funding The data collection for the Health Assets Project was supported by the Swedish Social Insurance Agency.
Competing interests None declared.
Ethics approval The HAP study was approved by the Ethics Committee at the University of Gothenburg (registration number 039-08) and conducted in accordance with the latest version of the Helsinki protocol.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement No additional data are available.