Participation bias in longitudinal studies: experience from the Population Study of Women in Gothenburg, Sweden

Scand J Prim Health Care. 2003 Dec;21(4):242-7. doi: 10.1080/02813430310003309-1693.


Objective: To describe a cohort study of women receiving a series of comprehensive health examinations over 32 years.

Design: Longitudinal population study based on a randomised sample of the female population from defined age cohorts.

Setting: City of Göteborg, Sweden.

Subjects: Subjects were 38, 46, 50, 54 or 60 years old at the start of the study in 1968. Re-examinations were performed in 1974, 1982 and 1992. Non-participants in the most recent examination, initiated in 2000, were offered home visits.

Main outcome measures: Participation, anthropometric and blood pressure changes.

Results: At the end of the 32-year follow-up, 64% of the original participants were alive, and low participation among survivors was a problem. An acceptable participation rate (71% of those alive) was obtained after home visits were offered. Surviving non-participants already had elevated cardiovascular risk factors at onset of the study in 1968, along with lower educational level and lower socioeconomic status. Home visited subjects were similar to non-participants with regard to anthropometry and blood pressure, but did not differ from participants with regard to social indicators. Thirty-two-year longitudinal data demonstrate clear ageing effects for several important variables, which should, however, be considered in the context of documented differences with non-participants at the baseline examination.

Conclusions: Longitudinal studies in elderly populations provide important data on changes during the ageing process. However, participation rates decline for a number of reasons and generalisations should be made with care. Moreover, including home visits in the protocol can both increase participation and reduce participation bias in elderly cohorts.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Anthropometry
  • Blood Pressure
  • Cohort Studies
  • Female
  • Humans
  • Longitudinal Studies
  • Middle Aged
  • Patient Selection*
  • Population Surveillance*
  • Selection Bias*
  • Sweden / epidemiology
  • Women's Health*