Trends in incidence rates of diagnosed attention-deficit/hyperactivity disorder (ADHD) over 12 years in Taiwan: A nationwide population-based study

We investigated time trends in the incidence rate (IR) of attention-deficit/hyperactivity disorder (ADHD) across the lifespan and potential factors affecting them using a Taiwanese population-based database. IR per 10,000 person-years (PY) of newly diagnosed ADHD based on ICD-9-CM was calculated annually for the total population, gender, 5 age groups, and 3 ADHD subtypes from 2000 to 2011. Among the 265,932 patients, IR increased from 7.92 to 13.92; the male-to-female ratio decreased from 3.61 to 2.90. The largest increase in IR was noted in young adults (19-30 years), followed by preschoolers (0-6 years), while the smallest increase was in adults ( > 31 years). The IR trends showed a more prominent increase in males than females among children, adolescents, and young adults, yet a reserved relationship existed among adults, with a more prominent increase in women. The combined type of ADHD exhibited a prominently increasing trend in the child/adolescent group (age <= 18) and the inattentive type ADHD in the adult group (age > 18). In conclusion, the ADHD IR is increasing with distinct differences among age, sex, and subtypes. The diminishing gap between those who need treatment and those actually treated might partly contribute to this trend, especially among young adults, preschoolers, and females.