Validity evidence
Justify what a score means and how it will be used
Validity concerns evidence supporting an intended score interpretation and use. Content evidence addresses domain coverage; construct evidence addresses theoretical meaning; criterion evidence relates scores to relevant outcomes, concurrently or prospectively. Convergent and discriminant evidence concern expected similarities and distinctions. Face validity is perceived plausibility, not strong validation. These are complementary lines of evidence, not independent certificates permanently attached to an instrument.
Use whenever scores will support substantive claims, decisions or comparisons, especially after changing language, population, mode of administration or the intended interpretation of a measure.
Strengths
- Connects statistical measurement to substantive meaning
- Identifies why apparently reliable scores may support poor decisions
Limitations
- External criteria may themselves be imperfect
- Evidence may not transfer across populations or uses
Know the boundary
Correlation with another questionnaire and high reliability cannot establish all forms of validity.