Table 1.

Baseline Characteristics of Participants by Level of Insomnia Score Among 142,933 Women at Enrollment in the Women's Health Initiative, United States, 1993–1998

Variable	Insomnia Score Level (WHIIRS)a								P Valueb
	0–3 (n = 39,607)		4–6 (n = 39,227)		7–10 (n = 36,427)		≥11 (n = 27,622)
	%	Mean	%	Mean	%	Mean	%	Mean
Age at baseline, years		62.5		63.1		63.4		63.3	<0.0001
Ethnicity, white non-Hispanic	81.3		83.0		84.8		82.9		<0.0001
Education, college graduate or above	44.2		40.5		38.4		32.0		<0.0001
Body mass indexc		27.6		28.0		28.0		28.4	<0.0001
Physical activity, METs/week		13.7		12.5		11.9		11.3	<0.0001
Smoking status									<0.0001
Never smokers	52.3		50.7		49.7		49.4
Former smokers	39.3		41.5		42.8		42.2
Current smokers	29.8		26.1		23.5		20.5
Alcohol intake, ≥7 drinks/week	10.9		11.6		12.3		11.6		<0.0001
Family history of cancer	44.6		46.7		47.5		48.0		<0.0001
Previous thyroid disease (yes)	21.0		23.5		25.0		25.1		<0.0001
Hormone therapy use									<0.0001
Estrogen alone	27.4		29.2		30.9		32.4
Estrogen plus progestin	23.1		21.7		21.1		19.5
Mixed use	5.2		5.6		5.9		5.8
Depression score (CES-D/DIS)
Mean score		0.01		0.02		0.04		0.10	<0.0001
Score ≥0.06	10.3		17.5		28.2		44.0		<0.0001

Abbreviations: CES-D, Center for Epidemiologic Studies Depression Scale; DIS, National Institute of Mental Health's Diagnostic Interview Schedule; METs, metabolic equivalents; WHIIRS, Women's Health Initiative Insomnia Rating Scale.

^a Sleep disturbance level was classified into 4 categories (WHIIRS: 0–3, 4–6, 7–10, and ≥11). The cutpoints were “quasi-quartiles” based on distribution of the ordinal scale 0–20 from WHIIRS.

^b P values were obtained from analysis of variance when the exposures were continuous and from chi-square tests when the exposures were categorical.

^c Weight (kg) / height (m)².