Prevalence estimates of neurodevelopmental disorders in Japan: A community sample questionnaire study

Aim: Prevalence estimates of neurodevelopmental disorders have been calculated by questionnaire surveys scored by a single rater, which introduces inherent rater biases. The present study aimed to estimate the prevalence and comorbidity rates of four neurodevelopmental disorders based on both parent and teacher rating scales. Methods: We performed a community sample survey recruiting 3852 children aged 6 to 9 years. Parents and teachers evaluated clinical conditions in children using questionnaire-style scales. These scales with cut-off values were used to estimate the prevalence and comorbidity rates of attention deficit hyperactive disorder, autism spectrum disorder, specific learning disorder (or developmental dyslexia), and developmental coordination disorder. Results: The prevalence estimates were separately confirmed according to the raters. Some estimates were higher than those in previous studies conducted in other countries. We also found a large disagreement between the parent and teacher rating scores. Moreover, the degree of agreement between two raters varied depending on the severity of the child's clinical condition. Conclusion: These estimates are the first findings based on evaluating children by two different raters. The prevalence and comorbidity estimates are informative for researchers and clinicians of pediatric neurology. The disagreements between two different raters raise questions about previous estimates of neurodevelopmental disorders.