Volunteerism and self-selection bias in human positron emission tomography neuroimaging research

Abstract

Scientists have known for decades that persons who volunteer for behavioral research may be different from those who decline participation and that characteristics differentiating volunteers from non-volunteers may vary depending on the nature of the research. There is evidence that volunteer self-selection can impact representativeness of samples in studies involving physically or psychologically stressful procedures, such as electric shocks, sensory isolation, or drug effects. However, the degree to which self-selection influences sample characteristics in “stressful” studies involving positron emission tomography (PET) has not been evaluated. Since estimation of population parameters, robustness of findings, and validity of inferred relationships can all be impacted by volunteer bias, it is important to determine if self-selection may act as an unrecognized confound in such studies. In the present investigation, we obtained baseline data on 114 M, F subjects who participated in a study involving completion of several self-report questionnaires and behavioral performance tasks. Participants were later given the opportunity to enroll in an [11C]raclopride PET study involving intravenous amphetamine (AMPH) administration. Demographic characteristics, personality traits, and task performance of subjects who consented to the latter study were compared with those who declined participation. Findings showed that the principal personality trait that distinguished the two groups was sensation-seeking; volunteers scored significantly higher on this dimension than non-volunteers. Males were more likely to volunteer than females. However, results of mediation analysis suggested that the relationship between gender and volunteer status was mediated by greater sensation-seeking traits in the males. Implications of these findings are discussed.

Who wants a free brain scan? Assessing and correcting for recruitment biases in a population-based sMRI pilot study

“…They also had higher cognitive test scores, fewer IADL impairments, and, over 6–8 years of follow-up, had significantly lower mortality rates than the randomly selected participants (Ganguli 1998). Using a different conceptual paradigm to study volunteerism and self-selection bias, a recent study (Oswald 2013) recruited by advertisement a sample of healthy young adults aged, assessed their demographic and personality characteristics, and offered them the opportunity to enroll in a positron emission tomography (PET) study involving intravenous amphetamine administration. Those who consented to this PET study were more likely to be male and to score significantly higher on sensation-seeking traits.…”

“…Since the characteristics of those who do not participate in a given study are typically unknown, the nature and extent of “volunteer bias” and “selection bias” are difficult to determine. Previous studies have shown that volunteers are younger, better educated, healthier, cognitively better than those randomly selected for research (Ganguli 1998; Jaramillo 2007); another study investigated personality traits of those who agreed to participate in a functional imaging study (Oswald 2013). How these factors actually influence the imaging study results is usually a matter for speculation.…”

Volunteer Bias in Research on Friendship Among Emerging Adults

“…They found that volunteers for the prison study had higher scores on aggression, authoritarianism, narcissism, and social dominance but lower scores on empathy and altruism. Recently, Oswald, Wand, Zhu, and Selby (2013) found that volunteers for a neuroimaging study had higher scores on sensation seeking compared to nonvolunteers. Collectively, there is convincing evidence to suggest that volunteers for research studies have certain experiences and characteristics that could threaten the generalizability of empirical studies.…”

Neural systems of cognitive demand avoidance

“…However, our fMRI participants consisted of a more variable sample who volunteered for fMRI scanning at different months of the year in response to ads placed around campus. A recent study showed that PET scan volunteers significantly scored higher in sensation-seeking trait compared to behavior-only volunteers (Oswald et al, 2013).…”