he extent to which an instrument adequately reflects the concept it is intended to measure. It involves evidence—often gathered through qualitative research—that the items and domains of the instrument are both appropriate and comprehensive for the intended measurement concept, target population, and use. Strong content validity confirms that the instrument truly captures what it is supposed to measure. Importantly, no amount of testing of other measurement properties (such as reliability or construct validity) can make up for poor content validity.
Example
A working group develops a questionnaire to assess fatigue in people with lupus. Through interviews and focus groups with patients and clinicians, they confirm that the questionnaire’s items fully cover the range of fatigue experiences—physical tiredness, mental exhaustion, and impact on daily life. This evidence supports the content validity of the instrument for that population.