ADHD and Hyperkinetic Disorder Symptoms in Australian Adults: Descriptive Scores, Incidence Rates, Factor Structure, and Gender Invariance

Objective: ADHD and Hyperkinetic Disorder (HKD) have the same 18 symptoms, covering inattention (IA), hyperactivity (HYP), and impulsivity (IMP). This study was aimed at providing descriptive scores for the different symptom groups in these disorders and how these scores varied by age and gender, the percentages of individuals meeting the symptom thresholds for the different ADHD types and HKD, the factor structure, and gender invariance of these symptoms in adults. Method: To accomplish this, 852 adults provided self-ratings for a scale comprising the 18 ADHD/HKD symptoms. Results: The findings showed that age and gender had minimal effects on the ADHD symptoms. Also, in terms of symptom counts, 2% had HKD and 6.3% had ADHD (inattentive = 1.6%, hyperactive-impulsive = 2.7%, and combined type = 2.0%). Confirmatory factor analysis (CFA) provided most support for the three-factor HKD model, involving separate factors for the IA, HYP, and IMP symptoms. This model showed full measurement invariance across gender. Conclusion: The theoretical and clinical implications of the findings are discussed.