One limitation to be discussed is that the ADHD and control groups both had average or higher IQ scores. There are two possible explanations for this finding. The most obvious is some degree of sample self-selection in our University setting (higher-IQ children or higher-IQ parents interested in participating in the study) or selection in who was lost due to motion artifact. We checked this last possibility by correlating IQ scores with movement (measured by mean frame-to-frame displacement), and found that IQ scores and movement were not correlated (r=−0.006, p value=0.95). While the relatively higher-than-average IQ scores of the sample and the supplementary analyses provide reassurance that low IQ scores do not account for the findings, it leaves unclear the extent to which the findings would generalize to a broader or lower functioning ADHD group.
