What does coefficient alpha measure?

Coefficient alpha, often referred to as Cronbach's alpha, is a statistical measure used to evaluate the reliability of a test. Specifically, it assesses the internal consistency of a set of measurements or items within a test. A high coefficient alpha value indicates that the items measure the same underlying concept and produce similar results when administered under the same conditions. This is crucial in appraisal practice, as ensuring the reliability of your assessment tools is essential for obtaining consistent and trustworthy results.

The focus of coefficient alpha is strictly on how consistently the test measures a concept, rather than measuring how well it captures what it is supposed to (validity), how it is scored, or how effective a teaching method may be. Each of those aspects—validity, scoring, and teaching effectiveness—relates to different dimensions of evaluation and assessment but does not pertain to what coefficient alpha specifically assesses.