. Author manuscript; available in PMC: 2013 Sep 11.

Published in final edited form as: Psychol Med. 2007 May 31;37(12):1703–1715. doi: 10.1017/S0033291707000815

Table 2.

Shared familial effects on ADHD and performance on the Fast Task

	Phenotypic correlation (95% CI)	Bivariate sibling correlation (95% CI)	Percentage of phenotypic correlation due to shared familial influences^a
Baseline MRT
Total sample	0·33 (0·26–0·40)	0·12 (0·02–0·22)	72
Male-only subsample	0·32 (0·19–0·47)	0·22 (0·07–0·37)	>100
Baseline s.d. of RTs
Total sample	0·40 (0·32–0·47)	0·13 (0·04–0·21)	63
Male-only subsample	0·41 (0·29–0·53)	0·21 (0·09–0·34)	>100
Baseline CV
Total sample	0·39 (0·32–0·47)	0·11 (0·04–0·19)	58
Male-only subsample	0·41 (0·30–0·52)	0·19 (0·08–0·30)	92

ADHD, Attention deficit hyperactivity disorder; CI, confidence interval ; MRT, mean reaction time; s.d., standard deviation; RT, reaction time; CV, coefficient of variation.

Under the assumption that familial effects are entirely due to genetic effects (see Discussion): percentage of phenotypic correlation due to shared familial influences=(2×bivariate sibling correlation)/phenotypic correlation.