Reliability depends on how much of the variation in scores is attributable to random or chance errors. A measure is valid when the differences in observed scores reflect true differences on the characteristic one is attempting to measure and nothing else. Validity and Reliability. If a measure is valid, it is reliable. Reliability is a necessary, but not a sufficient condition for validity.
Reliability only provides negative evidence of the validity of a measure.
Because it is so much more easily computed, reliability is often reported as evidence of validity. It is important to distinguish between the two concepts and to keep in mind that a measure may be reliable without being valid. Unfortunately, there are no shortcuts or easy ways to develop measures that are both valid and reliable. At DSS, we follow a seven step process to develop patient satisfaction measures. Specify Domain of the Construct.