Validity Health Dictionary

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.

An indication of how much a clinical test or sign is an accurate indicator of the presence of disease. Reduced validity may occur because (1) identical tests repeated on the same person in similar circumstances produce variable results;

(2) the same observer gets di?erent results on successive occasions – intraobserver error; (3) di?erent observers produce di?erent results.

n. an indication of the extent to which a measure (e.g. a clinical sign or test) is a true indicator of what it purports to measure (e.g. disease). Reduced validity can arise if the test produces different results when conducted several times on the same person under identical conditions (i.e. reduced reproducibility, reliability, or repeatability). This may be because the same observer gets different results on successive occasions (intraobserver error) or because a series of different observers fail to obtain the same result (interobserver error). Such errors may arise because of a true difference in observation and/or interpretation or because of a preconceived notion (often unconscious) by the observer, which influences his or her behaviour.