Validity is whether a study really measures what it claims to. Internal validity, question the validity, the validity of the test.
Internal validity asks whether the study shows what it says within itself; external validity asks whether the result carries beyond the sample. A study can be perfectly reliable — giving the same answer every time — and completely invalid, which is the distinction that catches people out. In law, validity means legal force. Note valid; and that the Latin means strength.
1nounvalidityWhether a study really measures what it claims to.
“Critics questioned the validity of the survey because it only asked people online.”
2nounforceLegal force.
“Lawyers challenged the validity of the contract because it had never been signed.”
validity is a quality of soundness.
Latin validitas comes from validus, strong, from valere, to be strong. Value, valour and prevail come from the same strength.
Proto-Indo-European
*h₂welh₁-
Latin
validitas
Middle French
validité
English, today
validity
From valid + ity, borrowed from Middle French validité, from Latin validitas.
Etymology from Wiktionary, CC BY-SA