Threats to the validity of locally developed multiple-choice tests in medical education: construct-irrelevant variance and construct underrepresentation.

Construct-irrelevant variance (CIV) - the erroneous inflation or deflation of test scores due to certain types of uncontrolled or systematic measurement error - and construct underrepresentation (CUR) - the under-sampling of the achievement domain - are discussed as threats to the meaningful interpretation of scores from objective tests developed for local medical education use. Several sources of CIV and CUR are discussed and remedies are suggested. Test score inflation or deflation, due to the systematic measurement error introduced by CIV, may result from poorly crafted test questions, insecure test questions and other types of test irregularities, testwiseness, guessing, and test item bias. Using indefensible passing standards can interact with test scores to produce CIV. Sources of content underrepresentation are associated with tests that are too short to support legitimate inferences to the domain and which are composed of trivial questions written at low-levels of the cognitive domain. "Teaching to the test" is another frequent contributor to CUR in examinations used in medical education. Most sources of CIV and CUR can be controlled or eliminated from the tests used at all levels of medical education, given proper training and support of the faculty who create these important examinations.