Relative Age Effect on ADHD Diagnosis, Medication Prescription, and Treatment Persistence: A Quasi-Experimental Study Within a Birth Cohort
Author(s)
Le Gao, PhD1, Min Fan, PhD2, David Coghill, MD3, Patrick Ip, MD2, Wallis Lau, PhD4, Kenneth Man, PhD4, Ian Wong, PhD2.
1Xi'an JiaoTong University, Shaanxi, China, 2The University of Hong Kong, Hong Kong, Hong Kong, 3University of Melbourne, Melbourne, Australia, 4UCL School of Pharmacy, London, United Kingdom.
1Xi'an JiaoTong University, Shaanxi, China, 2The University of Hong Kong, Hong Kong, Hong Kong, 3University of Melbourne, Melbourne, Australia, 4UCL School of Pharmacy, London, United Kingdom.
OBJECTIVES: To examine the impact of relative age on the diagnosis and/or medication prescription for attention deficit hyperactivity disorder (ADHD) in childhood and adolescence; and to investigate the relative age effect on ADHD treatment persistence in adolescence among children with ADHD.
METHODS: This is a quasi-experimental study involving children born between 2001 and 2010 in Hong Kong with follow-up until 2023. Children born in November and December were considered relatively younger, while those born in January and February were considered relatively older according to the Hong Kong school entry cut-off date (December 31). Cox proportional hazard model was used to evaluate the risk of being diagnosed with ADHD and/or being prescribed ADHD medication in childhood (6-12 years old) and adolescence (13-18 years old), adjusting for covariates at birth such as sex, socioeconomic status, birth year, preterm birth, small for gestational age, birth trauma, 5-minute Apgar score, and mode of delivery.
RESULTS: Compared to the relatively older group (n=33,971), children with relatively younger age (n=44,015) were more likely to be diagnosed with ADHD and/or prescribed ADHD medication during childhood (adjusted hazard ratio [HR]: 1.54; 95% confidence interval [CI]: 1.44-1.64), while a moderate effect is observed during adolescence (adjusted HR: 1.12; 95% CI: 0.90-1.39). Among those having ADHD in their childhood (n=11,747), children with relatively younger ages were less likely to be prescribed ADHD medications during adolescence (adjusted HR: 0.83, 95% CI: 0.76-0.90). Negative control analyses did not show any significant results.
CONCLUSIONS: The findings suggest that the relative age effect significantly influences the first ADHD diagnosis and/or medication prescription during childhood rather than adolescence. Furthermore, relatively younger children with ADHD are less likely to continue medication treatment during adolescence. Further research is warranted to explore the underlying mechanisms driving these associations and to develop targeted interventions for children with ADHD based on their relative age.
METHODS: This is a quasi-experimental study involving children born between 2001 and 2010 in Hong Kong with follow-up until 2023. Children born in November and December were considered relatively younger, while those born in January and February were considered relatively older according to the Hong Kong school entry cut-off date (December 31). Cox proportional hazard model was used to evaluate the risk of being diagnosed with ADHD and/or being prescribed ADHD medication in childhood (6-12 years old) and adolescence (13-18 years old), adjusting for covariates at birth such as sex, socioeconomic status, birth year, preterm birth, small for gestational age, birth trauma, 5-minute Apgar score, and mode of delivery.
RESULTS: Compared to the relatively older group (n=33,971), children with relatively younger age (n=44,015) were more likely to be diagnosed with ADHD and/or prescribed ADHD medication during childhood (adjusted hazard ratio [HR]: 1.54; 95% confidence interval [CI]: 1.44-1.64), while a moderate effect is observed during adolescence (adjusted HR: 1.12; 95% CI: 0.90-1.39). Among those having ADHD in their childhood (n=11,747), children with relatively younger ages were less likely to be prescribed ADHD medications during adolescence (adjusted HR: 0.83, 95% CI: 0.76-0.90). Negative control analyses did not show any significant results.
CONCLUSIONS: The findings suggest that the relative age effect significantly influences the first ADHD diagnosis and/or medication prescription during childhood rather than adolescence. Furthermore, relatively younger children with ADHD are less likely to continue medication treatment during adolescence. Further research is warranted to explore the underlying mechanisms driving these associations and to develop targeted interventions for children with ADHD based on their relative age.
Conference/Value in Health Info
2025-09, ISPOR Real-World Evidence Summit 2025, Tokyo, Japan
Value in Health Regional, Volume 49S (September 2025)
Code
RWD259
Topic Subcategory
Health & Insurance Records Systems
Disease
SDC: Pediatrics