Test validity refers to the degree to which evidence and theory exist to support the interpretation of test scores for particular purposes (AERA, APA and NCME, 2014). It is important to note that we validate a test score for a particular use (e.g., admission, placement), and that validity is not the property of a test in and of itself. This means that as opposed to talking about a test as simply valid or not valid, one should instead state, for example, “There is a great deal of validity evidence to support the use of The Character Skills Snapshot scores for independent school admission and/or placement decisions.” This also represents the notion that validity is a matter of degree and not absolute. It is therefore very important to gather validity evidence over time to either enhance, confirm or contradict previous findings.
Validity is a unified concept, yet there are multiple types of validity evidence that may contribute to the demonstration of validity. These types of evidence may include evidence based on test content—the relationship between the content of a test and the construct or characteristic it is intended to measure (Content Validity). Evidence based on internal structure refers to the degree to which test items and test components conform to the construct (e.g., score reliability, relationship of items and test dimensionality, etc.) (Construct Validity). Another type of validity evidence is based on relations to other variables, such as measures of criteria that the test is expected to predict (e.g., First Year GPA) or relationships to other tests measuring related constructs (Criterion Validity).