The risk of bias from omitted research

Evidence must be independently sought and free of economic interests

The rise of evidence based health care has highlighted the use of ineffective interventions, the risks of uncoordinated research, and the consequences of relying on studies published in prestigious journals while ignoring unpublished ones that have negative findings.1-5 Systematic reviews of the best evidence are now recognised as fundamental tools in overcoming these problems because they highlight questions that need urgent answers.6 But is evidence based health care achieving its goals? Aren't systematic reviews which are based on existing research at risk of amplifying the irrelevant? Should we be more concerned about “bias caused by omitted research” than the well recognised pitfall of publication bias?

The increasing awareness of this danger is leading to efforts to correct this imbalance. One such attempt is the Cochrane Collaboration (an international organisation named after Archie Cochrane, the British epidemiologist), which is committed to preparing, maintaining, and disseminating systematic reviews to map the value of healthcare interventions.7 The public and the media are attracted to alternative medicine, while doctors, who often criticise the use of these unproved …