the extent to which an instrument genuinely measures what it is intended to measure. An instrument must demonstrate that it is relevant (captures what matters for the target domain), comprehensive (covers all important aspects of the construct), and accurate (produces results that reflect reality) for the specified context and population.
Abbreviation: T
Example
If a questionnaire is designed to measure fatigue in people with rheumatoid arthritis, Truth means the items must genuinely capture the full experience of fatigue (not pain or mood), be relevant to patients’ lives, and accurately reflect changes over time. For example, questions about “level of tiredness after daily activities” would show high truth for fatigue, while questions about “number of steps walked” alone might not.