Reaction time variability in ADHD: a meta-analytic review of 319 studies.
Level 1 - systematic review of randomized trials
Meta-analysis of 319 studies (graded Level 1 by design analogy).
PubMed 23872284 · doi:10.1016/j.cpr.2013.06.001
What was done
Meta-analysis of 319 studies evaluating reaction time (RT) variability across children, adolescents, and adults with ADHD compared to typically developing (TD) controls, clinical controls, and within-subject conditions (ADHD subtypes, treatment, and motivational effects). Random-effects models were applied with corrections for measurement unreliability and publication bias.
What was found
Individuals with ADHD exhibited greater RT variability than TD controls in both child/adolescent (Hedges' g = 0.76) and adult cohorts (g = 0.46). Psychostimulant treatment attenuated RT variability (g = -0.74), whereas non-stimulant medications and psychosocial interventions showed no effect. RT variability deficits remained after controlling for mean RT, but mean RT differences disappeared after controlling for RT variability. Adolescents and adults with ADHD did not differ in RT variability from clinical control groups, and children with ADHD were only slightly more variable than clinical controls (g = 0.25).
Why it matters
This review establishes that intra-individual RT variability—rather than general processing speed slowing—is a core feature of ADHD that responds robustly to stimulants, while clarifying that it functions as a broad transdiagnostic marker rather than an ADHD-specific cognitive deficit.
Limits
The abstract does not disclose total participant counts or specific task paradigms. The finding that RT variability does not reliably distinguish ADHD from other clinical control groups limits its utility as a standalone diagnostic biomarker.
Cited by
- supports Increased intra-individual response time variability during tasks is a hallmark feature of individuals diagnosed with ADHD.