Effect of relative age on childhood mental health: A cohort of 9,548,393 children and adolescents

Background The effect of relative age on the diagnoses of attention deficit hyperactivity disorder (ADHD), disruptive behavior disorder (DD), anxiety disorder, and depressive disorder and the prescription for ADHD and antidepressant medications remains unclear. Aim To clarify the impact of relative age in a school year with the diagnoses of ADHD, DD, anxiety disorder, and depressive disorder and the prescription for ADHD and antidepressant medications. Methods The annual cutoff birthdate for entry to school in Taiwan is August 31. The Taiwan National Health Insurance Research Database was used to enroll 9,548,393 children and adolescents aged 3-17 years during the study period (September 1, 2001, to August 31, 2011). The Poisson regression model was performed to examine the likelihood of receiving diagnoses of ADHD, DD, anxiety disorder, and depressive disorder, as well as the prescription of ADHD and antidepressant medications among children born in August (the youngest) and September (the oldest). Results Both boys and girls born in August had a higher risk of being diagnosed as having ADHD (odds ratio [OR] = boys: 1.65, girls: 1.80), DD (1.29, 1.45), anxiety disorder (1.49, 1.33), and depressive disorder (1.10, 1.10). Furthermore, children born in August were more likely to be prescribed ADHD medication (1.71, 1.72) and antidepressants (1.18, 1.09) compared with those born in September. Discussion Relative age, as an indicator of neurocognitive maturity, is a critical factor for the likelihood of being diagnosed as having ADHD, DD, anxiety disorder, and depressive disorder among children and adolescents.