Table 2.

The outcome and related information included in this meta-analysis.

Author	Year	Data collection	Breast cancer ascertainment	Sleep duration (h/d) and risk (95% CI)	Adjusted variable	Quality assessment
Xiao et al. [9]	2016	Questionnaire	State cancer registries; pathology reports; medical records	<6: 1.09 (0.83–1.44) 6: 1.01 (0.78–1.30) 7: 1.19 (0.92–1.53) 8: reference ≥9: 1.07 (0.80–1.43)	Age, enrollment year, enrollment state, race, education, income, marital status, BMI, physical activity, overall sitting, smoking, pack-year, number of live birth, age at first birth, length of breastfeeding, age at menarche, menopause status, hormone therapy, multivitamin, aspirin, diabetes, family history of cancer, alcohol consumption, and dietary intakes of total fat, fiber, folate and total calories	8
Hurley et al. [10]	2015	Questionnaire	California cancer registry	3–6: 0.97 (0.91–1.04) 7–9: reference ≥10: 1.13 (0.86–1.50)	Race/ethnicity, alcohol consumption, menopausal status, hormone therapy use	6
Wang et al. [11]	2014	Face-to-face interview	Medical records	≤6: 1.62 (1.18–2.21) 6.1–8.9: reference ≥9: 1.58 (1.18–2.12)	Age, education, BMI, age at menarche, menopausal status, parity, physical activity, breastfeeding, family history of breast cancer, other sleep factors	7
Vogtmann et al. [12]	2013	Interview	Pathology reports; medical records	≤5: 0.89 (0.80–1.00) 6: 0.92 (0.85–0.98) 7: reference 8: 1.00 (0.93–1.07) ≥9: 1.05 (0.92–1.20)	Age, clinical trial arm assignment, number of live births, age at menarche, age at menopause, BMI, energy expenditure, education, income, race/ethnicity, marital status, age at first birth, use of hormone therapy, history of benign breast disease, family history of breast cancer, alcohol consumption, smoking status	8
Wu et al. [13]	2012	In-person interview	National cancer registry	≤6: reference 7: 1.00 (0.84–1.19) 8: 1.00 (0.84–1.21) ≥9: 0.89 (0.64–1.22)	Age, year, dialect group, education, parity, BMI, menopausal status	8
Girschik et al. [14]	2012	Self-administered postal questionnaire	Western Australian cancer registry	<6: 1.04 (0.83–1.32) 6-7: 0.95 (0.79–1.14) 7-8: reference >8: 1.05 (0.83–1.33)	Age, number of children, age at first birth, breastfeeding, menopausal status, use and duration of hormone therapy, alcohol consumption, comparative weight at the age of 30 years, melatonin, physical activity	8
Kakizaki et al. [15]	2008	Questionnaire	Miyagi prefectural cancer registry	≤6: 1.67 (1.002–2.78) 7: reference 8: 0.99 (0.59–1.65) ≥9: 0.29 (0.09–0.98)	Age, BMI, history of disease, family history of cancer, marital status, education, alcohol consumption, time spent walking, caloric intake, menopausal status, age at menarche, age at first delivery, number of deliveries, oral contraceptive drugs, hormone drug	8
Pinheiro et al. [16]	2006	Mailed questionnaire	Blinded medical chart review	≤5: 0.93 (0.79–1.09) 6: 0.98 (0.91–1.06) 7: reference 8: 1.05 (0.97–1.13) ≥9: 0.95 (0.82–1.11)	Age, BMI, height, history of benign breast disease, family history of breast cancer, parity and age at first birth, age at menarche, postmenopausal hormone use, physical activity, alcohol, caloric intake, smoking	7
McElroy et al. [17]	2005	Telephone interviews	State cancer registries	<5: 0.94 (0.62–1.44) 5–5.9: 0.82 (0.65–1.05) 6–6.9: 0.89 (0.79–1.01) 7–7.9: reference 8–8.9: 1.01 (0.91–1.11) ≥9: 1.01 (0.84–1.23)	Age, state, parity, age at first full-term pregnancy, family history of breast cancer, alcohol consumption, BMI, menopause status, age at menopause, postmenopausal hormone use, marital status	8
Verkasalo et al. [18]	2005	Questionnaires	Finnish cancer registries	≤4: 0.88 (0.11–6.91) 5: 0.91 (0.36–2.32) 6: 0.74 (0.44–1.27) 7: 0.81 (0.60–1.10) 8: reference 9: 0.64 (0.40–1.02) ≥10: 0.65 (0.24–1.75)	Age, zygosity, social class, number of children, use of oral contraceptives, BMI, alcohol use, smoking, physical activity	8