Validity

Validity: Validity refers to whether something measures what it proports to be measuring, i.e. any random cup in your cabinet may be able to reliably measure the same volume of liquid over and over, but just because it is called a cup does not mean it is a valid measure of a "cup" of fluid.

• Types of validity:
  • Face validity - measures what it appears to measure; that it is possible.
    • Example, is it plausible that the Ely's Test is an assessment of Rectus Femoris length.
  • Content validity - does it measure all aspects of a content domain.
    • Example, with regard to most assessments and tests in human movement science, content validity is achieved via the combination of face validity, anatomical knowledge and knowledge of relevant research.
  • Criterion validity - justifies the validity of the measuring instrument by comparing it to a gold standard.
    • Example, the degree markings on a goniometer may be compared to a standard protractor to ensure accuracy.
  • Construct validity - the ability of an instrument to measure an abstract concept.
    • Example, does a glutues maximus manual muscle test give an indication of an individuals ability to walk up stairs.