Validity (psychometric)

In psychometrics a valid measure is one which is measuring what it is supposed to measure. Validity implies reliability (accuracy). A valid measure must be reliable, but a reliable measure need not be valid.

Validity may be assessed by correlating measures with a criterion measure known to be valid. When the criterion measure is collected at the same time as the measure being validated the goal is to establish concurrent validity; when the criterion is collected later the goal is to establish predictive validity. A measure has construct validity if it is related to other variables as required by theory. Content validity, or face validity, is simply a demonstration that the items of a test are drawn from the domain being measured; it does not guarantee that the test actually measures phenomena in that domain.

Predictive or concurrent validity cannot exceed the square of the correlation between two versions of the same measure.

copyright 2004