Schwartz 1997.

Methods	Case‐control study
Participants	60 cases/485 controls Aged 18 to 44 years
Interventions	Combined oral contraception: current use, past use, none use, norethindrone, norgestrel
Outcomes	Ischemic stroke Events: current use 6/46, past use 39/363, none use 52/424, norethindrone 4/32, norgestrel 1/14
Notes	USA
Risk of bias
Bias	Authors' judgement	Support for judgement
Exposure ascertainment	High risk	COC use not objectively confirmed.
Outcome assessment	High risk	Ischemic stroke not objectively confirmed.
Follow‐up	Unclear risk	Not applicable as this was a case‐control study.
Source population	High risk	Controls from a different source population to the cases.