Cultural and contextual differences on how ADHD symptoms are perceived, as opposed to aetiological differences, may occur between countries. In the current study, cross-country differences in parental reporting of ADHD symptoms in Australia, Norway, Sweden and the US were examined.
A population-based sample of preschool-aged twins from the four countries were followed into early school age. The Disruptive Behaviour Rating Scale (DBRS)* was used to obtain parent and teacher ratings of 18 symptoms of ADHD according to the Diagnostic and Statistical Manual of Mental Disorders – 4th Edition. Cognitive variables (verbal memory, naming speed and visuospatial skill) were used at the end of preschool to test the external validity of ADHD in each country.
One twin from each pair was randomly selected to control for non-independence. In total, 253 participants were recruited from Australia, 482 from the US, and 239 from Norway/Sweden (Scandinavia). Since Scandinavian participants were generally a few months older than children in Australia and the US at the end of preschool, age effects were controlled for. At the end of preschool and in early school age, ADHD symptom severity was higher in males than in females in all countries (p < 0.05). Four hypotheses were tested to explain potential cross-country differences.
Hypothesis 1: context
- Using parental report, at the end of preschool, mean (standard deviation [SD]) symptom level of total ADHD was significantly (p < 0.01) higher in Australia (13.6 [8.1]) and the US (12.9 [8.3]) compared with Scandinavia (10.3 [7.1]).
- Mean (SD) for total ADHD symptoms was also significantly (p < 0.01) higher in Australia (10.5 [7.0]) and the US (9.4 [7.7]) than in Scandinavia (7.2 [6.8]) at the end of the second grade.
- Since country differences were also present at the end of the second grade, this finding did not support the context hypothesis, i.e. raters for all countries would report similar levels of ADHD symptoms once the literacy practices were more comparable.
Hypothesis 2: genuine aetiologic differences not due to artefacts
- Internal validity analyses indicated a lack of measurement equivalence between Scandinavia and Australia and the US. This suggests that raters in Scandinavia used the ADHD rating scale differently. Consequently, the genuine aetiologic differences hypothesis was rejected.
Hypothesis 3: under-reporting tendency
- The internal consistency of the DBRS was calculated for symptom dimensions and total severity ratings per parental report; however, as the internal consistency was similar across countries, a tendency for under-reporting was not supported.
Hypothesis 4: over-reporting tendency
- A comparison of effect sizes for high levels of ADHD symptoms across countries showed that Scandinavia had a larger effect size (d = 0.36–1.12) compared with Australia or the US (d = 0.06–0.47).
- The external validity correlations for verbal memory, naming speed and visuospatial skill were higher in Scandinavia than in Australia or the US:
- Scandinavia: r = –0.24 (p < 0.001), r = –0.22 (p < 0.001) and r = –0.16 (p < 0.05), respectively
- Australia: r = –0.06 (p > 0.05), r = –0.16 (p < 0.01) and r = –0.05 (p > 0.05), respectively
- US: r = –0.12 (p < 0.05), r = –0.08 (p < 0.15) and r = –0.12 (p < 0.01), respectively.
- Since stronger external validity of ADHD ratings was associated with Scandinavia, this suggests that reporting of behavioural problems is more accurate and indicates that there is a tendency to over-report symptoms of ADHD in Australia and the US.
There were several possible limitations to this study. Firstly, the team in Scandinavia mainly recruited families in rural areas, while the variance in families in Australia was less and had a bias towards higher socioeconomic status. Secondly, as the materials had to be translated from English into Norwegian and Swedish, translation effects may represent a limitation. Thirdly, the study only included younger children from preschool to second grade, which may limit these findings.
The authors indicated that these results suggest that parental reporting of ADHD symptoms may be more accurate in Norway and Sweden compared with Australia and the US. These findings may have clinical and educational implications for how parental reporting of ADHD informs diagnoses in these four countries.
*The scale has two dimensions with nine symptoms each to assess ‘inattention’ and ‘hyperactivity and impulsivity’. Each symptom is rated on a 4-point scale, where 0 = never or rarely, 1 = sometimes, 2 = often, 3 = very often. Items that are scored as 2 or 3 indicate positive symptoms, and those scored as 0 or 1 indicate negative symptoms
MacDonald B, Pennington BF, Willcutt EG, et al. Cross-country differences in parental reporting of symptoms of ADHD. J Cross Cult Psychol 2019; 50: 806-824.