Letters
The pill and thrombosis
Study subject to unmeasured confounders and biases
BMJ 2011; 342 doi: https://doi.org/10.1136/bmj.d3349 (Published 31 May 2011) Cite this as: BMJ 2011;342:d3349
- Anne Szarewski, clinical senior lecturer1,
- Diana Mansour, clinical director2
- 1Wolfson Institute of Preventive Medicine, Queen Mary, University of London, London EC1M 6BQ, UK
- 2Newcastle Hospitals Community Health, New Croft Centre, Newcastle upon Tyne NE1 6ND, UK
- a.szarewski{at}qmul.ac.uk
The papers on venous thromboembolism in oral contraceptive users have similar faults to earlier database studies.1 2 These include lack of validation of venous thromboembolism (VTE) cases and lack of information on, or control of, important potential confounders such as duration of use, especially short duration use; family history; body mass index (BMI); and smoking.3 Jick and Hernandez’s …
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