Abstract
BackgroundParticipation 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.MethodsThe 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.ResultsCompared 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).ConclusionsSignificant demographic and clinical differences were found between OCS participants and non-participants. Extrapolation of research findings to other populations should be undertaken cautiously.
Highlights
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
As of September 2009, 3106 consented participants were enrolled in the Ontario HIV Treatment Network Cohort Study (OCS), of whom 2925 had completed at least one annual questionnaire
85% were male, the median age was 46 (IQR 40–52), 72% were Caucasian, 71% were men having sex with men (MSM), 12% were infected with HIV through injection drug use, the median CD4 count was 471 (IQR 330–650) and 73% had viral load < 50 copies/ml at the time of OCS consent, which was a median of 0 days (IQR 0, 59) before the date of completing the first questionnaire (Table 1)
Summary
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. Before generalizing the results of a Population-based studies using non-nominal data from administrative databases or medical charts have been invaluable in HIV research for determining incidence, prevalence and natural history of specific HIV-related conditions [4,5,6,7,8]. While these studies undergo ethics review, individual patient consent is not usually required, so that participation bias does not influence the composition of the study sample. These studies provide important insights into the dynamics and interplay of clinical HIV disease with social factors, the time commitment to complete the questionnaires and willingness to share personal details may yield a study sample which is not representative of the population from which it is drawn
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