studies that rely on patient reported outcomes. It refers to the potential of a subject's views, values, or expectations changing over the course of a study, thereby adding another factor of change on the end results. Clinicians and healthcare providers must recalibrate surveys over the course of a study to account for Response Shift Bias. The degree of recalibration varies due to factors based on the individual area of investigation and length of study. Statistical variation In a study by Norman et al. about health-related quality of life surveys, it was found that most survey results were within a half standard deviation. Norman et al. theorized that this is due to the limited human discrimination ability as identified by George A. Miller in 1956. Utilizing the Magic Number of 7 ± 2, Miller theorized that when the scale on a survey extends beyond 7 ± 2, humans fail to be consistent and lose ability to differentiate individual steps on the scale because of channel capacity. Norman et al. proposed health-related quality of life surveys use a half standard deviation as the statistically significant benefit of a treatment instead of calculating survey-specific "minimally important differences", which are the supposed real-life improvements reported by the subjects. In other words, Norman et al. proposed all health-related quality of life survey scales be set to a half standard deviation instead of calculating a scale for each survey validation study where the steps are referred to as "minimally important differences". See also Medical law Patient-reported outcome Pharmacoeconomics Medical ethics References External links ProQolid (Patient-Reported Outcome & Quality of Life Instruments Database) Mapi Research Trust ("Non-profit organization involved in Patient-Centered Outcomes") PROLabels(Database on Patient-Reported Outcome claims in marketing authorizations) Quality-of-Life-Recorder (Project to bring QoL measurement to routine practice. Platform & library of electronic questionnaires, Shareware/Freeware) The International Society for Quality of Life Health and Quality of Life Outcomes The Healthcare Center. Better Health for Everyone Health care Medical terminology Healthcare