Cronbach’s alpha

Cronbach’s alpha is a coefficient (a number between 0 and 1) that is used to rate the internal consistency (homogeneity) or the correlation of the items in a test. A good test is one that assesses different aspects of the trait (e.g. depression) being studied. If a test has a strong internal consistency most measurement experts agree that it should show only moderate correlation among items (.70 to 0.90). If correlations between items are too low, it is likely that they are measuring different traits (e.g. both depression and quality of life items are mixed together) and therefore should not all be included in a test that is supposed to measure one trait. If item correlation are too high, it is likely that some items are redundant and should be removed from the test.

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