Representativeness of an HIV cohort of the sites from which it is recruiting: results from the Ontario HIV Treatment Network (OHTN) cohort study
1 Toronto General Research Institute, University Health Network, Room 13EN226, 200 Elizabeth St., Toronto, Ontario, M5G 2C4, Canada
2 Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
3 Ontario HIV Treatment Network, Toronto, Ontario, Canada
4 Department of Medicine and Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Ontario, Canada
5 Division of General Internal Medicine, Centre for Research on Inner City Health, The Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Ontario, Canada
6 The Ottawa Hospital Division of Infectious Diseases, The University of Ottawa, Ottawa, Ontario, Canada
7 Windsor Regional Hospital, Windsor, Ontario, Canada
8 Department of Psychiatry, University of Toronto, Toronto, Ontario, Canada
9 Maple Leaf Medical Clinic, Toronto, Ontario, Canada
10 Women’s College Research Institute, Women’s College Hospital, Toronto, Ontario, Canada
BMC Medical Research Methodology 2013, 13:31 doi:10.1186/1471-2288-13-31Published: 5 March 2013
Participation bias is a well-known phenomenon in epidemiologic research, where individuals consenting to research studies differ from individuals who are not able or willing to participate. These dissimilarities may limit the generalizability of results of research studies. Quantification of the participation bias is essential for the interpretation of research findings.
The Ontario HIV Treatment Network Cohort Study (OCS) is an ongoing open cohort study of HIV positive individuals receiving care at one of 11 sites in Ontario. OCS participants from 4 sites were compared to non-participants (those who declined or were not approached) at those sites with regard to gender, age, HIV risk factor, CD4 count and viral load (VL). Generalized logit regression models were used to identify predictors of declining to participate or not being approached to participate.
Compared to participants (P) in the OCS, individuals who declined to participate (D) and those who were not approached (NA) were slightly younger (D:45, NA:44 vs P:46), less likely to be male (D: 71%, NA:75% vs P:88%), less likely to be Caucasian (D:41%, NA:57% vs P:72%) and less likely to be Canadian-born (D: 39%, NA: 52% vs P: 69%). Patients who were not approached to participate were less likely to have VL < 50 copies/mL than other patients (D: 75%, NA: 62%, P: 74%) and had lower CD4 counts than OCS participants (D: 450 cells/mm3, NA: 420 cells/mm3, P: 480 cells/mm3).
Significant demographic and clinical differences were found between OCS participants and non-participants. Extrapolation of research findings to other populations should be undertaken cautiously.