Slow drift rate predicts ADHD symptomology over and above executive dysfunction.

Slow drift rate has become one of the most salient cognitive deficits among children with ADHD, and has repeatedly been found to explain slow, variable, and error-prone performance on tasks of executive functioning (EF). The present study applies the diffusion model to determine whether slow drift rate better predicts parent and teacher ratings of ADHD than standard EF metrics. 201 children aged 8-12 completed two tests of speeded decision-making analyzed with the diffusion model and two traditionally scored tests of EF. Latent EF and drift rate factors each independently predicted the general ADHD factor in a bifactor model of ADHD, with poor EF and slow drift rate associated with greater ADHD symptomology. When both EF and drift rate were entered into the model, slow drift rate (but not EF) continued to predict elevated symptomology. These findings suggest that using drift rate to index task performance improves upon conventional approaches to measuring and conceptualizing cognitive dysfunction in ADHD. Implications for future cognitive research in ADHD are discussed.