it was also notable that on all of these tasks the group with ADHD showed more variable performance than the controls.
the measure of variability was the standard deviation of the reaction times for the primary task; there were substantial effect sizes for this group difference, ranging from 0.52 for the reversal task to 2.45 for the SST.
moreover, although group differences in SSRT were not statistically significant, the ADHD group was three times more variable in terms of this measure than the controls.