Table 3 -.

Results from weighted analyses^*

	‘76-’82 cohort			‘96-’00 cohort			Combined cohorts
Outcome	Est. 95% CI	P		Est. 95% CI	P	Interaction P	Est. 95% CI	P
ADHD	1.12 (0.73, 1.70)	0.610		1.29 (0.86, 1.92)	0.215	0.632	1.21 (0.91, 1.60)	0.184
Learning disability	0.93 (0.70, 1.25)	0.644		1.08 (0.74, 1.60)	0.679	0.542	0.98 (0.78, 1.23)	0.870
Reading LD	0.98 (0.69, 1.39)	0.925		0.96 (0.59, 1.57)	0.876	0.942	0.98 (0.73, 1.30)	0.872
Mathematics LD	0.93 (0.67, 1.29)	0.667		0.93 (0.58, 1.49)	0.762	0.997	0.93 (0.71, 1.22)	0.600
Written language LD	0.98 (0.71, 1.35)	0.890		1.39 (0.84, 2.29)	0.200	0.251	1.07 (0.83, 1.39)	0.596
IEP-SL	1.10 (0.66, 1.85)	0.713		0.82 (0.52, 1.30)	0.408	0.409	0.93 (0.65, 1.34)	0.716
IEP-EBD	0.89 (0.47, 1.68)	0.718		0.56 (0.23, 1.39)	0.212	0.418	0.72 (0.40, 1.30)	0.280

^*Results are from inverse probability for treatment weighted (IPTW) stratified proportional hazards regression. Robust sandwich estimates for covariance were used to account for the weighted approach. Estimates are hazard ratios associated with single exposure to anesthesia prior to age 3 compared to no exposure. For each outcome, one model was run to assess the interaction effect between cohort membership and anesthesia exposure and a second model was run without the interaction effect to estimate the effect of anesthesia in the combined cohort. The interaction p-value is testing the hypothesis that the effect of single exposure is equal between the 2 cohorts. Stabilized weights were calculated according to sex and cohort membership. Missing data was accounted for by using multiple imputation. Twenty imputed datasets were generated and analysis results were combined using Rubin’s rules to account for uncertainty in the imputed values. Est, estimate; CI, confidence interval; ADHD, attention-deficit hyperactivity disorder; LD, learning disability; IEP, individualized education plan; SL, speech/language; EBD, emotional/behavioral disorder.