Table 3. Kappa scores for test-retest reliability of sleep questions in the Breast Cancer Environment and Employment Study sleep questionnaire.

Usual sleep habits question (n)	Kappa	P-value
Duration of sleep on work days (n = 192)	0.71	<0.001
Duration of sleep on non-work days (n = 192)	0.71	<0.001
Ever been diagnosed with a sleep disorder (n = 194)	0.69	<0.001
Ever taken melatonin to help you sleep (n = 192)	0.62	<0.001
Do you consider yourself a good sleeper (n = 187)	0.74	<0.001
Did you ever fall asleep with the light on (n = 187)	0.64	<0.001
- Did you usually leave it on all night (n = 66)	0.78	<0.001
Did you ever sleep with an eye mask (n = 186)	0.45	<0.001
Ever experienced periods of sleep disturbance ​ in lifetime (n = 186)	0.60	<0.001
Number of periods of sleep disturbance ​ in lifetime (n = 184)	0.59	<0.001