Abstract
The rates of enrollment of volunteers for brain magnetic resonance imaging (MRI) studies vary by demographic and clinical characteristics. We use data from a large MRI study to identify factors associated with differential enrollment and to examine potential biases this may produce in study results. Results from recruitment of 1,431 women into the MRI substudy of the Women's Health Initiative Memory Study (WHIMS-MRI) are described. A sensitivity analysis was conducted to estimate the degree of bias associated with missing data on estimates of risk factor relationships. Of 2,345 women contacted from an established cohort of women older than 70 years of age, 72% consented to undergo screening for WHIMS-MRI. Scanning was ultimately completed on 61%. Completion rates varied according to a range of sociodemographic, lifestyle, and clinical characteristics that may be related to study outcomes. Plausible levels of selective enrollment in magnetic resonance imaging studies may produce moderate biases (< +/-20%) in characterizations of risk factor relationships. Adverse events, such as claustrophobia, occurred during 1.7% of the attempted scans and, in 0.8% of instances, led to lost data. Enrollment of older women into brain imaging studies is feasible, although selection biases may limit how well study cohorts reflect more general populations.
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