THERAPEUTIC PERSONALITY BIAS:
When a therapists convictions about efficacy systematically influence both outcomes (positive personality) and their measurements (desire for positive results)1. This bias may occur in a medical research study when the treatment/exposure assignment is known to the person measuring the outcome (e.g. an unblinded study). Further, this bias is potentially made worse in an unblinded study when the person involved in the measurement of study variables, such as the outcome, has a conflict of interest with the treatment (e.g. financial or other relationship with the manufacturer/supplier of the treatment etc.). Also see: Information Bias, and Bias Due to Conflicts of Interest.
Reference:
1. Sackett DL. Bias in analytic research. J Chronic Dis. 1979;32 (1-2):51-63. (Link to Reference)