Michaelsson 1999.

Methods	Case‐control study; 6 counties in Sweden
Participants	Postmenopausal women, age 50 to 81 years; descriptions of cases and controls below
Interventions	Oral contraceptive use
Outcomes	Hip fracture Insufficient data for analysis; results presented as reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Case definition and representativeness	Low risk	Cases: 1644 women with fractures of proximal femur that occurred between October 1993 and February 1995 Used clinical records or operation registers in all 24 hospitals in study area; residents in study area, born after 1913 Index date for cases: date of fracture Fracture data from clinical records or operation registers in 24 hospitals Excluded: women with fracture due to malignant disorder (26), high‐energy trauma (4), incorrect diagnosis (51), blindness (5), birth outside Sweden (202), severe alcohol abuse, psychosis, or dementia (576), or death within 3 months of fracture (123)
Exposed cohort: representativeness	Unclear risk	Not applicable
Control selection and definition; non‐exposed cohort selection	Low risk	Controls: 4059 Swedish‐born women, randomly selected from national population register the month before study. Index date for controls: 95 days before mailing of first questionnaire. 70 to 80 years old, frequency‐matched (2 per case) to age distribution of hip fracture cases in county of residence 50 to 69 years old, frequency‐matched to expected number of breast cancer cancers to be used in breast cancer study (same questionnaire); yielded 2 to 4 controls per fracture case in each 5‐year age group and county of residence
Exposure ascertainment, including same method for cases and controls	Low risk	OC use via mailed questionnaire; for cases, sent after fracture, mean 95 + 23 days; for controls, sent on 6 occasions during study Questionnaire focused on reproductive history and use of exogenous sex hormones, including OCs and HRT. Included anthropometry, education, profession, dietary habits, alcohol consumption, cigarette smoking, physical activity (at childhood, ages of 18 and 30, and recent years), and medical history (stroke, diabetes mellitus, cardiovascular diseases, and inflammatory bowel disease). Half of participants were contacted by telephone for missing information. Questions: dose and type of OCs used and dates of use Recall aided by picture charts of all preparations commonly used in Sweden during 1950 to 1995. Picture chart, with more detailed questionnaire, sent to women who indicated OC use in first questionnaire. All women responded to second questionnaire.
Outcome assessment (cohort study): method and evidence outcome not present at study start	Unclear risk	Not applicable
Comparability of groups on basis of design or analysis	Low risk	Multivariate analysis using logistic regression adjusted for covariates that "slightly affected" OR (age, body mass index, HRT, parity) Previous hip fracture examined; did not affect OR. Excluded from analysis those who reported natural menses (premenopausal): 1 case and 50 controls.
Case‐control: non‐response rate	Low risk	Responses: cases, 1328/1644 (81%); controls, 3312/4059 (82%) Of responses, those solely by phone (less extensive interview): cases, 202/1328 (15%); controls, 497/3312 (15%)
Cohort: follow‐up length and adequacy (including loss to follow‐up)	Unclear risk	Not applicable