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Trends in participation rates in case–control studies of occupational risk factors 1991–2017
  1. Jeavana Sritharan1,
  2. Yang Luo2,
  3. M Anne Harris1,2,3
  1. 1Occupational Cancer Research Centre, Cancer Care Ontario, Toronto, Ontario, Canada
  2. 2School of Occupational and Public Health, Ryerson University, Toronto, Ontario, Canada
  3. 3Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Dr M Anne Harris, School of Occupational and Public Health, Ryerson University, Toronto, ON M5B 2K3, Canada; anne.harris{at}


Objective Declining participation has been observed in previous epidemiological studies, could occupational risk factor epidemiology be particularly vulnerable to this trend? The objective of this study was to assess trends of participation rates in occupational case-control studies.

Methods Five prominent occupational and epidemiological journals were pre-selected and all articles published between 1991 and 2017 were screened for case-control studies of occupational risk factors for chronic disease outcomes. The primary independent variable was median year of data collection, while the primary outcome variable was reported participation rate. We conducted linear regression, adjusting for study characteristics that included study gender mix, location of recruitment, disease outcome, and data collection method.

Results A total of 180 studies published in the five journals were included in the final analysis. The mean participation was higher for cases (78.9%) than for controls (71.5%). In linear regression, a significant trend of decreasing participation was observed for both cases with a percent change of −0.50 per year (95% CI −0.75 to −0.25) for cases and a percent change of −0.95 per year (95% CI −1.23 to −0.67) for controls. After adjustment for study gender mix, location, disease outcome, and data collection method, the trend remained statistically significant for both case and control groups.

Conclusion Declining participation rates in case-control studies of occupational risk factors may reflect an overall decline of participation in population-based samples. Lower participation rates introduce the potential for bias and may deter future population-based studies of occupational risk factors.

  • case-control
  • occupational risk factor
  • participation rates
  • epidemiologic studies
  • bias

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  • Contributors JS, YL and MAH provided substantial contributions to the conception of the work, acquisition, analysis and interpretation of the data. All three authors drafted the work, approved the final version to be published, and agreed to be accountable for all aspects of the work ensuring the accuracy and integrity of the work submitted.

  • Funding This study was supported by start-up funding provided to the PI (MAH) by Ryerson University (Toronto, Canada).

  • Competing interests None declared.

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data used in the study are from existing and available online peer-reviewed publications. The data relevant to the study is included in the paper and any additional information is uploaded as online supplementary information.