This study provides evidence that all research workers are not uniformly successful in their evaluation of the clinical effectiveness of new drugs. It is not the province of this paper to enter into factors that are responsible for the wide variations of attitudes and success displayed by various workers, but it is suggested that both conscious and unconscious factors determine how any given individual will report the efficacy of a drug.There is need to record the characteristics of the research worker as carefully as the other elements of the research design. The bias of a single investigator may in some cases be offset by using multiple evaluators.Abstract Teaser