Table 3.

Variance component analysis of sleep parameters

Parameter	Wake time (n = 723)		Bedtime (n = 723)		Sleep duration (n = 723)		MEQ scorec (n = 625)		ESS scored (n = 723)
	% Variance ± SE	P	% Variance ± SE	P	% Variance ± SE	P	% Variance ± SE	P	% Variance ± SE	P
Fixed effectsa	0.30	< 0.0001	0.16	< 0.0001	0.19	< 0.0001	0.10	< 0.0001	0.13	< 0.0001
Heritabilityb	0.20 ± 0.09	0.007	0	NS	0	NS	0.21 ± 0.09	0.002	0.17 ± 0.08	0.008
Shared householdb	0.27 ± 0.07	< 0.0001	0.72 ± 0.03	< 0.0001	0.38 ± 0.06	< 0.0001	0	NS	0	NS

^aAge, sex, season, occupation, total activity, and sleep activity. Percent variance shown.

^bAdjusted for fixed effects listed above.

^cMorningness-Eveningness Questionnaire.

^dEpworth Sleepiness Scale.