The quality of being logically or factually sound, or legally acceptable. It can also mean how well a test or method measures what it is supposed to measure.
From French 'validité', from Latin 'validitās' (strength, soundness), from 'validus' (strong). It has been in English since the 1500s.
Validity is the 'strength level' of arguments, documents, or tests. In research, a test can be reliable (consistent) but still have low validity if it consistently measures the wrong thing.
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