Selection bias in enrollment to a programme aimed at the secondary prevention of ischaemic heart disease in general practice: a cohort study.

OBJECTIVE

To evaluate differences between adults who participated in a secondary prevention of ischaemic heart disease (IHD) programme and those who did not.

DESIGN

Population-based cohort study.

SETTING

A random selection of 12 Irish general practices.

PARTICIPANTS

A total of 493 adults with IHD identified in 2000/2001.

INTERVENTION

Medical records search and postal questionnaires in 2000/2001 and 2005/2006.

MAIN OUTCOME MEASURES

Differences in demographic characteristics and indicators of process of care and risk factor management between participants and non-participants.

RESULTS

Multiple logistic regression confirmed that female gender was associated with a reduced likelihood of participation in the secondary prevention programme [odds ratio (OR) 0.53 (95% CI: 0.32-0.87)], while an adequately controlled total cholesterol level was associated with an increased likelihood of enrollment [OR 1.82 (95% CI: 1.18-2.80)].

CONCLUSIONS

There is limited evidence that biases, which have been shown to affect participation in research, also affect participation in care programmes in everyday practice. A gender bias appears to have affected the enrollment of participants for the secondary preventive programme considered by this study, with enrollment favouring men with well-managed cholesterol. Reimbursement dependent upon patient adherence may incentivise the enrollment of adherent patients, although the influence of patient choice is unclear: the need to maintain records relating to patients who opt out of such interventions is thus highlighted.