CDISC-Gloss – The extent to which a variable (for example, a rating scale) measures what it is supposed to measure. [ICH E9 Glossary] evidence from qualitative research demonstrating that the instrument measures the concept of interest, including evidence that the items and domains of an instrument are appropriate and comprehensive, relative to its intended measurement concept, population, and use. NOTE: Testing other measurement properties will not replace or rectify problems with content validity. [FDA Final PRO Guidance]