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Alpha is also a function of the number of items, so shorter scales will often have lower reliability estimates yet still be preferable in many situations because they are lower burden. An alternative way of thinking about internal consistency is that it is the extent to which all of the items of a test measure the same latent variable. The ...
Internal and external reliability and validity explained. Uncertainty models, uncertainty quantification, and uncertainty processing in engineering; The relationships between correlational and internal consistency concepts of test reliability; The problem of negative reliabilities
Cronbach's alpha (Cronbach's ), also known as tau-equivalent reliability or coefficient alpha (coefficient ), is a reliability coefficient and a measure of the internal consistency of tests and measures. [1] [2] [3] It was named after the American psychologist Lee Cronbach.
E.g. a scale that is 5 pounds off is reliable but not valid. A test cannot be valid unless it is reliable. Validity is also dependent on the measurement measuring what it was designed to measure, and not something else instead. [6] Validity (similar to reliability) is a relative concept; validity is not an all-or-nothing idea.
The modern models reorganize classical "validities" into either "aspects" of validity [3] or "types" of validity-supporting evidence [1] Test validity is often confused with reliability, which refers to the consistency of a measure. Adequate reliability is a prerequisite of validity, but a high reliability does not in any way guarantee that a ...
The validity of a measurement instrument or psychological test is established through experiment or correlation with behavior. Reliability is established with a variety of statistical techniques, classically through an internal consistency test like Cronbach's alpha to ensure sets of related questions have related responses, and then comparison ...
In the case when scores are not tau-equivalent (for example when there is not homogeneous but rather examination items of increasing difficulty) then the KR-20 is an indication of the lower bound of internal consistency (reliability). The formula for KR-20 for a test with K test items numbered i = 1 to K is
Internal validity, therefore, is more a matter of degree than of either-or, and that is exactly why research designs other than true experiments may also yield results with a high degree of internal validity. In order to allow for inferences with a high degree of internal validity, precautions may be taken during the design of the study.