ADHD and working memory: Reviewing causes for a consistent correlation

Working memory capacity negatively correlates with Attention Deficit Hyperactivity Disorder. In this narrative review, we examine the strength of this correlation, alongside explanations for its existence. Some explanations cast working memory weaknesses as an artifact of testing, such that inattention during testing disrupts encoding. Other explanations link working memory weakness to poor executive control and selective attention, such that ADHD impedes mental manipulation central to all working memory tasks. We thereafter compare these extant explanations against the following alternative explanation: Correlations between ADHD and working memory are artifacts of contaminated samples employing imprecise inclusion and exclusion criteria that neither commonly control for intelligence nor rule out low intelligence as an alternative explanation for putative ADHD. This alternative explanation is relevant because intelligence positively correlates with working memory capacity; and at the same time, ADHD samples are often selected based on ratings that neither measure intelligence nor attention. This alternative explanation suggests that, though not spurious, the correlation between these constructs is exaggerated by including those with lower intelligence in ADHD samples. We systematically select a subset of ADHD studies, scrutinizing their methodology, discussion, and limitations sections so as to determine, where possible, whether working memory weaknesses remain after controlling for intelligence.