Selection Bias in a Study of Implantable Defibrillator Patients: The Role of Type D Personality

BACKGROUND Selection bias constitutes a major issue in research using volunteers as study participants. PURPOSE We examined whether research in partners may affect participation rates of implantable cardioverter-defibrillator (ICD) patients with a Type D personality (joint presence of negative affectivity and social inhibition). METHOD Patients who underwent ICD implantation between May 2003 and November 2007, and who had a partner, were included (n = 440). In September 2005, a substudy on partners of ICD patients was added (n = 276 patients). RESULTS The proportion Type D patients after the start of the partner substudy was significantly lower as compared to the proportion before this substudy (17.5% versus 28.8%; p = 0.006). Patients who participated following the start of the partner substudy were less likely to have a Type D personality (OR = 0.44; p = 0.002), adjusting for possible confounders. In the partner substudy, nonparticipation was more prevalent among partners of Type D patients as compared to partners of non-Type D patients (20.4% versus 10.1%; p = 0.044). Partner nonparticipation was marginally significantly associated with Type D personality of the patient (OR = 2.13; p = 0.083), adjusting for confounders. CONCLUSIONS The addition of a partner substudy may be related to a decreased proportion of participants with a Type D personality. Nonparticipation was more prevalent among partners of Type D patients. These observations may influence results of studies, as Type Ds tend to be less healthy.