The older the better: are elderly study participants more non-representative? A cross-sectional analysis of clinical trial and observational study samples

Objective Study participants can differ from the target population they are taken to represent. We sought to investigate whether older age magnifies such differences, examining age-trends, among study participants, in self-rated level of activity compared to others of the same age. Design Cross-sectional examination of the relation of participant age to reported ‘relative activity’ (ie, compared to others of the same age), a bidirectionally correlated proxy for relative vitality, in exemplars of randomised and observational studies. Setting University of California, San Diego (UCSD) Participants 2404 adults aged 40–79 including employees of UCSD, and their partners (San Diego Population Study, observational study). 1016 adults (aged 20-85) not on lipid medications and without known heart disease, diabetes, cancer or HIV (UCSD Statin Study, randomised trial). Measurements Self-rated activity relative to others’ age, 5-point Likert Scale, was evaluated by age decade, and related via correlation and regression to a suite of health-relevant subjective and objective outcomes. Results Successively older participants reported successively greater activity relative to others of their age (greater departure from the norm for their age), p