The extent to which a measurement, test or study measures what it purports to measure. There are various types of validity: construct validity: The degree to which an instrument measures the characteristic being investigated; the extent to which the conceptual definition matches the operational definition. content validity: Verification that the method of measurement actually measures what it is expected to measure, covering all areas under investigation reasonably and thoroughly. criterion validity: Verification that the instrument correlates with external criteria of the phenomenon under study, either concurrently or predictively. external validity: The extent to which study results can be generalized beyond the sample used in the study. face validity: A type of content validity, determining the suitability of a given instrument as a source of data on the subject under investigation, using commonsense criteria. internal validity: the extent to which the effects detected in a study are truly caused by the treatment or exposure in the study sample, rather than being due to other biasing effects of extraneous variables.... validity
Generally, that branch of medicine concerned with diseases that do not require surgery, specifically the study and treatment of internal organs and body systems; it encompasses many subspecialties.... internal medicine
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