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

Selection bias constitutes a major issue in research using volunteers as study participants.

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).

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).

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.

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.