The Bias Methods Group (BMG) is one of 13 Cochrane Methods Groups world-wide comprised of individuals with an interest and expertise in the science of systematic reviews. This group strives to raise awareness of the problem of bias and is exploring important questions with respect to the epidemiology of research results and outcomes. The Cochrane BMG is also investigating a range of different forms of bias such as ‘publication bias’, language bias’, and ‘outcome variable bias’.