Definition: An assessment is valid if it measures what it purports to measure. A statement or conclusion regarding the relationship between two or more variables is valid if it is backed by sound and rigorous research.
Why it matters: If an assessment states that it measures a numeracy skill that predicts success in later math classes but it does not actually measure the skills it claims to measure or if that skill is not really a good predictor of later success, then the test is invalid. Using invalid tests is a waste of time and money because no one is sure what it measures, if anything, or what it means if it does measure something.
Example of use: Always check the validity of a assessments and the predictive claims of those assessments.
Rumrill Jr, P. D., Cook, B. G., & Wiley, A. L. (2011). Research in special education: Designs, methods, and applications. Charles C. Thomas, Publisher, Ltd. 2600 South First Street, Springfield, IL 62704.