Intraindividual variability (IIV) refers to reaction time (RT) variation across the trials of a given cognitive task. Little research has contrasted different measures of IIV or assessed how many RT trials are required to provide a robust measure of the construct. We, therefore, investigated three measures of IIV (raw SD, coefficient of variation, and intraindividual SD statistically removing time-on-task effects) in relation to frontal white matter hyperintensities (obtained through structural MRI) in 415 cognitively normal community-dwelling adults aged 44 to 48 years. Results indicated the three IIV measures did not differ greatly in predictions of white matter hyperintensities, although it is possible that time-on-task effects were influential. As few as 20 trials taking approximately 52 s to administer provided a reliable prediction of frontal white matter hyperintensities. We conclude that future work should evaluate the comparative utility of different IIV measures in relation to persons exhibiting clear neuropathology. (JINS, 2013, 19, 1–6)
