Letters Combined oral contraceptives and venous thromboembolism

Oral contraceptive study omitted several confounders

BMJ 2015; 350 doi: http://dx.doi.org/10.1136/bmj.h3303 (Published 24 June 2015) Cite this as: BMJ 2015;350:h3303
  1. Samuel S Zagarella, dermatologist
  1. 1Concord Hospital, Sydney, Australia
  1. samuelzagarella{at}gmail.com

An important methodological problem may affect the findings of this otherwise well conducted case-control study.1

Although the authors included polycystic ovarian syndrome as a confounder, they did not include acne or hirsutism in the …

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