Study designs of evaluations included in the review
Controlled studies, in which the risk of venous thrombosis for women who had used oral contraceptives as a method of birth control had been estimated, were included if the index group was compared to a control group and the outcome assessed objectively. The primary studies selected were of the following designs: case-control, follow-up studies and a randomised controlled trial (RCT). Excluded were case series, studies controlled by general population data, and reports in which data for venous thrombosis could not be differentiated from data for arterial thrombosis.
Where data were reported more than once, only the original or the final results were included.
Specific interventions included in the review
The interventions included oral contraceptives, typically containing more than 50 microg of oestrogen.
Participants included in the review
The participants were women aged between 15 and 44 years who had experienced a venous thrombosis while taking the combined oral contraceptive pill.
Outcomes assessed in the review
The main outcome assessed was the occurrence of an objectively-confirmed venous thrombosis, including rarely occurring thromboses such as neurological, ophthalmic and mesenteric.
How were decisions on the relevance of primary studies made?
The authors do not state how the papers were selected for the review, or how many of the authors performed the selection.