Related Experiment Video
Updated: Jun 22, 2026
Generalized Psychophysiological Interaction (PPI) Analysis of Memory Related Connectivity in Individuals at Genetic Risk for Alzheimer's Disease
Published on: November 14, 2017
MRI substudy participation in Alzheimer disease (AD) clinical trials: baseline comparability of a substudy sample to
Rema Raman1, Ronald G Thomas, Michael W Weiner
1Department of Neurosciences, University of California San Diego, La Jolla, 92093-0717, USA. reraman@ucsd.edu
Objective:
To determine if a self-selected group of participants who enroll in an imaging substudy of Alzheimer disease (AD) clinical trials is representative of the overall study sample.
Methods:
Baseline data from 2 ongoing AD clinical trials with 402 and 313 randomized participants were analyzed. Magnetic resonance imaging substudy enrollers (166 participants in trial 1 and 161 participants in trial 2) and nonenrollers were compared on baseline demographic, medical and clinical characteristics separately for the 2 trials.
Results:
In both trials, enrollers were statistically similar to nonenrollers on most demographic and clinical measures. One study sample showed that enrollers had lower cognitive scores at baseline when compared with nonenrollers: lower Mini Mental State Examination scores (20.15+/-3.6 vs. 21.04+/-3.6, P=0.02), and higher Alzheimer's Disease Assessment Scale-cognitive domain scores (24.99+/-8.5 vs. 23.03+/-9.3, P=0.03); however, the difference was not considered clinically important and was not observed in the second trial.
Conclusions:
The groups of individuals who agreed to participate in the imaging substudies of AD trials were remarkably comparable to the comparison groups at baseline on a wide range of demographic and clinical measures; there seems to be a minimal effect of self-selection bias. The results indicate that it may be reasonable to generalize findings in an imaging substudy to the complete the study population.
