Brief report: ADHD Rating Scale-IV (parent/caregiver-report) norms for young Danish schoolchildren

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Objective The Attention-Deficit/Hyperactivity Disorder Rating Scale-IV (ADHD-RS-IV) assesses ADHD symptoms in children and adolescents. The original United States norms comprise percentiles. Yet, no Nordic percentile norms exist, and only T-scores, which (often falsely) assume normally distributed data, are currently available. Here, we for the first time provide Danish percentile norms for children aged 6–9 based on parent/caregiver-reports, and illustrate the potential consequences of T-scores when derived based on the expected skewed distribution of an ADHD scale in the population. Materials and methods The sample comprised 1895 Danish schoolchildren (879 girls and 1016 boys) in 1st, 2nd, or 3rd grade from the general population. Their parents/caregivers completed the ADHD-RS-IV. Sex and age differences were investigated, percentiles were derived based on the observed score distributions, and for comparison, T-scores > 70 were estimated, which are expected to identify the top 2.3% under the assumption of normality. Results Boys were rated to have higher ADHD-RS-IV scores than girls except on the impulsivity score. No age effects were found on the majority of scores. Sex-stratified and unisex percentiles (80, 90, 93, 98) were reported. The distribution of ADHD-RS-IV scores were highly skewed. T-score cutoffs identified a significantly higher proportion of and about twice as many children as having elevated ADHD symptoms than expected (4.3–5.2% vs. 2.3%). Conclusions ADHD-RS-IV (parent/caregiver-report) percentile norms for young Danish schoolchildren are now available for future reference. The use of percentiles is considered appropriate given the skewed score distribution and since T-scores appear to over-identify children as having clinically elevated ADHD symptoms.