Table 1.

Criteria for risk of bias assessment.

Criteria	Low risk	High risk	Unclear risk
Study design	Prospective or retrospective cohort, nested case-control	Case-control	Information not reported
Adjustment of confounders	Adjusted for 4 or more of the following: age, education/income, family history of cancer, hormone therapy use/oral contraceptive use/reproductive history, smoking status, and alcohol consumption	Adjusted for 3 or less of the following: age, education/income, family history of cancer, hormone therapy use/oral contraceptive use/reproductive history, smoking status, and alcohol consumption	Information not reported
Selection of participants and their eligibility criteria	Studies clearly stating their eligibility criteria and the sources and methods of selection of participants	Studies not clearly stating their eligibility criteria and the sources and methods of selection of participants	Information not reported
Measurement of predictor variables	Identified through objective measures	Self-reported or pharmaceutical prescriptions	Information not reported
Breast cancer diagnosis	Histologically confirmed or identified through cancer registry/medical records	Self-reported	Information not reported
Study size	Large enough for adequate power	Not large enough for adequate power	Information not reported
Handling of missing data	Missing data analysis specified	Missing data deleted from analysis	Information not reported
Reasons for nonparticipation of individuals at each stage of the study	Reasons clearly reported for each stage of study	Reasons not reported for each stage of study	Information not reported