Different clinical conditions are of interest to different clinical populations. For each condition, measures are needed to cover different aspects of care. Most importantly, reports on clinical performance for consumers should include text educating consumers about the care that is recommended by clinical practice guidelines and the outcomes that can be expected for each condition. The external agency collects the performance measurements, verifies their accuracy, and presents comparisons among similar providers of care. For a measure to be valid, it must be low in both random and systematic error.
Validity includes reliability, which is the extent to which the measure is low in random error.
An unreliable measure, therefore, cannot have high validity. Reliability of a measure captures how consistently it performs when applied. Reliability and validity of a measure are determined with regard to the intended use of the measurement. For instance, a patient survey may have been validated as a measure of health status. This does not mean that this survey is valid as a measure of quality of clinical performance.