Validity: “ refers to the extent to which a test usefully measures the construct or trait it was designed to evaluate. There are several kinds of test validity, including :

–face validity (the extent to which test items appear appropriate to the individual taking the test), – content validity (the extent to which items in the test sample the relevant domain of interest), and

– criteria-related validity (the extent to which the test score produces evidence of concurrent and predictive validity).

–Concurrent validity estimates are produced when test scores and external criteria measures are evaluated at the same time and may be divided into convergent and discriminant validity:  

1. convergent validity:  the degree to which test scores are strongly related to other measures of the same construct, and

2. discriminant validity: the degree that test scores differ substantially from scores obtained on measures of unrelated constructs, respectively.

–Predictive validity: The concept of predictive validity is based on circumstances in which test scores are obtained, and the individual’s performance on relevant criteria is evaluated at some later date.

–Incremental validity – does a measure add to the prediction of a criterion above what can be predicted by other sources of data?

Sechrest in 1963 (per Hunsley and Meyer, 2003) first argued that, in addition to evidence for convergent and discriminant validity, a psychological test that was intended for applied uses) must yield an improvement in prediction compared with the result derived from using data that are easily and routinely obtained as part of the process of assessment (e.g., over brief case history information, simple biographical data, and brief interviews).

— “All of these measures of reliability and validity may be seen as establishing a known error rate for a test…” (Archer et. al. )