Evidence-based medicine and randomized double-blind clinical trials: a study of flawed implementation

The randomized double-blind clinical trial (RDBCT) is a key source of infor mation for evidence-based medicine. However, anomalous and unexplainable re sults have prompted suggestions that 'unknown and unidentifiable biases' ma y exist. This paper identifies that a possible flaw in the implementation o f RDBCTs may account for these biases. The flaw relates to the breaking of the double blind through the generation of beliefs and expectations in expe rimenters. These, in turn, may lead to unconscious biases in assessment and cues to patients. It is then uncertain how much of an observed effect is d ue to such expectations or the treatment itself. Therefore, any RDBCT in wh ich the maintenance of blinding is not monitored throughout its course is a t risk of its conclusions being compromised. It is not sufficient to assert that blinding must have been maintained through arguments based on design features. The burden of proof is on the researchers to demonstrate, through data, that blinding has been maintained. The need to address social psycho logical issues in implementing RDBCTs is discussed and it is recommended th at to avoid this confound, methods of monitoring and accounting for experim enter beliefs and expectations should be routinely included in future RDBCT s.