Validity

The word validity is primarily a measurement term, having to do with the relevance of a measuring instrument for a particular purpose, but it has been broadened to apply to an entire study. A research investigation is said to have internal validity if there are valid causal implications and is said to have external validity if the results are generalizable.

As far as measurement is concerned, the most important property of a measuring instrument is the extent to which it has been validated with respect to some gold standard whose validity has been assumed to be taken for granted. For example, if scores on a test of mathematical aptitude (the instrument to be validated) correlate highly with scores on a subsequent test of mathematical achievement (the ...