Table 2. The risk of ADHD^a among exposed participants compared to matched unexposed participants.

Outcome	No. of ADHD /No. of accumulated PY × 10,000 (incidence rate/10,000 PY)		Absolute rate difference/10,000 PY (95% CI)	HR (95% CI)b	aHR (95% CI)b,c	aHR (95% CI)b,d
	Exposed group	Unexposed group
ADHD	1,994/46.8 (42.6)	1,318/47.6 (27.7)	14.88 (12.49–17.28)	1.519 (1.416–1.628)	1.490 (1.387–1.601)	1.406 (1.302–1.519)

ADHD = attention deficit hyperactive disorder, PY = person-years, HR = hazard ratio, CI = confidence interval, aHR = adjusted hazard ratio.

^aADHD was defined as at least a principal diagnosis of 10th revision of the International Classification of Diseases code F90.X after 72 months of age.

^bA Cox proportional hazards model was used to assess the relationship between general anesthesia and later development of ADHD. HRs and 95% CIs of ADHD in relation to previous general anesthesia exposure, using time after the index date as the underlying time scale, were calculated.

^cAdjusted for sex, age at index date, calendar year of birth (2008 or 2009), birth residence (Seoul/metropolitan, city, or rural area), and economic status (low, middle, or high).

^dAdjusted for sex, age at index date, calendar year of birth (2008 or 2009), birth weight, birth residence (Seoul/metropolitan, city, or rural area), economic status (low, middle, or high), and perinatal disease.