BMJ  2005;331 (22 October), doi:10.1136/bmj.331.7522.0-c

Ethics may lead to bias: consent

Adults who consent to participate in observational research differ from those who do not or cannot consent. This can bias disease registers, epidemiological studies, and health services research. Al-Shahi and colleagues (p 942) analysed the differences in a prospective, population based cohort study of all adults with newly diagnosed brain arteriovenous malformation over a three year period. When non-consenters (those who didn't give explicit consent, or refused to participate in the study) were excluded from the analysis, the important finding that initial presentation with intracranial haemorrhage conferred a significantly higher risk of subsequent haemorrhage during follow-up was lost.

Credit: RON SUTHERLAND/SPL

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Relevant Article

Bias from requiring explicit consent from all participants in observational research: prospective, population based study

Rustam Al-Shahi, Céline Vousden, Charles Warlow for the Scottish Intracranial Vascular Malformation Study (SIVMS) Steering Committee
BMJ 2005 331: 942. [Abstract] [Full Text] [PDF]