How Persistent is ADHD into Adulthood? Informant Report and Diagnostic Thresholds in a Female Sample
Although the notion that Attention-Deficit/Hyperactivity Disorder (ADHD) often persists into adulthood is increasingly accepted, important diagnostic questions remain. Using a large (baseline proband n = 140, comparison n = 88) prospectively followed, ethnically diverse female sample, I examined the impacts of (a) informant (i.e., parent- vs. self-report) and (b) diagnostic symptom threshold (i.e., the DSM-IV 6/9 symptoms of inattention [IA] or hyperactivity/impulsivity [H/I] vs. a developmentally referenced criterion [DRC]) on estimates of ADHD persistence from childhood (age range 6-12) into young adulthood (mean age = 19.6 years). Further, I assessed and compared the predictive validity of ADHD status per each informant, as well as via the two different symptom cutoffs, on measures assessing functioning in a number of important domains (e.g., depression, academic achievement, global impairment).
Separate 2 x 2 (Wave 1 diagnostic status x Wave 3 diagnostic status) chi-square analyses revealed that per parent-report, significantly more probands (44%) than baseline comparison participants (1%) met full ADHD criteria (χ2  = 42.51, p< 0.001, φ = 0.47). Significantly more probands (22%) than comparisons (2%; (χ2  = 15.97, p< 0.001, φ = 0.28) met full criteria via young adult self-report as well. Informant diagnostic concordance was significant, but of a small effect size (κ; = .22). Using a series of hierarchical multiple regression analyses and controlling for key covariates, parent-reported ADHD was found to be independently associated with poorer outcomes on eight of nine considered measures (|β|'s ranging from 0.18 to 0.61). Self-reported ADHD was independently associated only with lower math scores (|β| = .18).
As in past research, the DRC was set at two SD above the comparison participants' mean symptom number, yielding a diagnostic threshold of 4/9 H/I and 5/9 IA symptoms. Via the DSM-IV cutoff, ADHD was estimated to persist in 55.9% of baseline probands; via the DRC, this estimate rose to 61.4%. One-way ANCOVA models were used to test mean differences on outcome measures for participants who met the DSM-IV threshold, those who only met the DRC ("DRC-only"), and those who met neither threshold. All models were significant (all Fs >6.50, all ps < .01). DRC-only participants endorsed poorer outcomes of large to very large effect sizes across seven of the study's nine outcome measures, compared to participants who met neither cutoff. Further, DRC-only participants did not differ on any outcome measure from those who met the higher DSM-IV threshold.
The present findings add to extant research in suggesting that (a) parent-report yields higher ADHD persistence estimates than young adult self-report and (b) parent-reported persistence remains a more potent predictor of young adult functioning than self-report. Findings also suggest that self-reported ADHD persistence rates may be higher in young adult females than in males, although this suggestion merits further investigation. Further, findings suggest that a lower symptom threshold than that traditionally used in clinical nomenclatures (i.e., than a threshold identical to that of child-based diagnosis) may be more developmentally appropriate in young adults.