Table 1.

Participant characteristics and stop-signal task outcome measures

	ADHD		Siblings		Controls		Wald-χ2	Cohen’s d	p-value	Between group effects
Males	129		48		55
Females	56		63		69		28.1	.536	<.001	ADHD < Sibs = Controls
	Mean	SD	Mean	SD	Mean	SD
ADHD Symptomsa	12.9	3.1	1.3	3.4	0.6	1.5	242.7	2.34	<.001	ADHD > Sibs = Controls
Age (yr)	17.3	3.2	17.3	4	16.5	3.3	1.6	.124	.44
Estimated IQb	95.3	16.8	102.4	15.9	107.1	14.5	38.2	.633	<.001	ADHD < Sibs < Controls
Education (yr)	12.82	2.14	12.82	2.22	13.52	1.91	6.387	.249	.041	ADHD = Sibs < Controls
Age range	8–25		8–27		9–23
IQ rangeb	55–138		56–144		58–141
	Mean	SD	Mean	SD	Mean	SD
SSRT (ms)c	268.1	59.4	254.1	49	258.2	52.6	6.012	.241	.046	ADHD > Sibs = Controls
RTV (ms)c	112	38.3	93.2	36.7	82.2	30.8	30.03	.555	<.001	ADHD > Sibs > Controls
Errors (n)c	6.3	7.6	4.2	5.6	3.1	3.5	13.56	.365	<.001	ADHD > Sibs = Controls
Medication use (%)	54		0		0		160.64	1.571	<.001	ADHD > Sibs = Controls
Comorbid ODDd	55		4		0		67.68	.876	<.001	ADHD > Sibs = Controls
Comorbid CDd	12		0		0		15.62	.393	<.001	ADHD > Sibs = Controls
Comorbid RDd	34		11		11		7.33	.267	.026	ADHD > Controls

Note: ADHD = attention deficit/hyperactivity disorder; ODD = oppositional defiant disorder; CD = conduct disorder; RD = Reading disability SSRT = stop-signal reaction time; RTV = reaction time variance; Errors = number of errors on go-trials. Bolded values indicate significant effects.

^aADHD diagnosis was based on K-SADS structured psychiatric interviews and Conners’ questionnaires (58).

^bEstimated IQ was based on the block-design and vocabulary subtests of the Wechsler Intelligence Scale for Children (WISC) or Wechsler Adult Intelligence Scale (WAIS-III) (59).

^cTask effects for the stop-task derived from generalized estimate equation models, using a significance threshold of p<.05 and correcting for familiality, gender age and IQ.

^dODD, CD and RD diagnosis was based on K-SADS structured psychiatric interviews (60).