Table 3.

Within-pair associations between drinking and measures of learning and attention with and without propensity score adjustment.

Measure	Unadjusted				Propensity Score-Adjusted
	Estimate	95% CI	t-statistic	p-value	Estimate	95% CI	t-statistic	df	p-value
Overall Learning	−0.624	[−0.964 — −0.283]	3.59	<.001	−0.609	[−0.949 — − 0.268]	3.50	48.1	.001
Learning Over Trials	−0.449	[−0.753 — −0.145]	2.90	.004	−0.447	[−0.752 — − 0.141]	2.87	48.1	.006
Trial 5 Total	−0.161	[−0.259 — −0.063]	3.23	.001	−0.158	[−0.257 — − 0.060]	3.16	48.1	.003
Trial 1 Total	−0.035	[−0.107 — 0.037]	0.95	.342	−0.032	[−0.104 — 0.040]	0.88	48.1	.383
Trial B Total	−0.063	[−0.139 — 0.013]	1.63	.103	−0.061	[−0.136 — 0.015]	1.56	48.1	.124

Note: Estimate is the parameter estimate for the within-pair effect and 95% the 95% confidence interval around it, obtained by means of the cluster-robust sandwich estimator of standard errors in svyglm, adjusted for any effects of age cohort, sex and zygosity. Estimates in the right-hand portion of the table are propensity score-adjusted estimates of the within-pair effect. Propensity score indicators were all from the age-11 assessment (see Table S2). Missing values were imputed 50 times, a propensity score estimated for each imputation set, and cotwin-control analyses were conducted on each set using inverse probability of treatment weighting (IPTW). Results of the 50 sets of IPTW-weighted analyses were combined as using the procedure outlined by Rubin [39]. df are corrected as recommended by Barnard and Rubin [2].