The degree to which a result is likely to be true and free of bias. There are many types of validity:
- Concurrent – Scores on an assessment should be related to scores on a previously-validated measure of the same or similar construct/concept.
- Construct – The assessment measures content related to the theoretical definition of the assessment's purpose (the construct/concept). For example, items on a depression assessment measure should address the diagnostic criteria for depression.
- Content – Similar to construct validity. Assessment items should address the full range of the criteria for the construct/concept being measured.
- Convergent – Scores on assessments designed to measure the same construct (e.g., different depression assessment measures) should be positively correlated.
- Criterion – Scores on an assessment should relate to or predict outcomes relevant to its theoretical construct/concept. For example, an assessment of mathematical aptitude should predict performance in a mathematics class.
- Divergent – Measures of constructs/concepts that are not theoretically related (e.g., age and intelligence) should not be correlated across different scales.
- External validity – External validity is the extent to which the results of a study can apply to people other than the ones that were in the study. This is a measure of how generalizable the results are to others outside of the study.
- Face validity – Items on an assessments should appear to the reader to measure what the assessment is designed to measure. Note: However, for some assessments intended to measure socially undesirable traits or behaviors, concealing the nature of the assessment may make it a more valid measure of the construct. For example, an assessment of abusive behavior might not contain the term "abuse," but might focus instead on specific acts.
- Internal validity – Internal validity is the extent to which a study properly measures what it is meant to.