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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.
Internal consistency is usually measured with Cronbach's alpha, a statistic calculated from the pairwise correlations between items. Internal consistency ranges between negative infinity and one. Coefficient alpha will be negative whenever there is greater within-subject variability than between-subject variability. [1]
The most common internal consistency measure is Cronbach's alpha, which is usually interpreted as the mean of all possible split-half coefficients. [9] Cronbach's alpha is a generalization of an earlier form of estimating internal consistency, Kuder–Richardson Formula 20. [9]
The Cronbach's alpha was used to obtain reliability measures. Across one group of nine studies, alpha measures were 0.71-0.89, reflecting good internal consistency. The test adequately measures for depressive symptoms. [1] In another group of 16 studies of test-retest reliability, alpha measures were reported as 0.38–0.87. [1]
Cronbach's alpha, [25] for example, is designed to assess the degree to which multiple tests produce correlated results. Perfect agreement is the ideal, of course, but Cronbach's alpha is high also when test results vary systematically. Consistency of coders’ judgments does not provide the needed assurances of data reliability.
Multiple convenience and random samples, as well as research studies in both clinical and nonclinical sample [22] [1] [23] Internal consistency (Cronbach's alpha, split half, etc.) Good Cronbach's alpha reported at .88 for measuring depression [22] Inter-rater reliability: Good Kappas range from .64-.81 for depression. [24] Kappa for anxiety is ...
It is a special case of Cronbach's α, computed for dichotomous scores. [2] [3] It is often claimed that a high KR-20 coefficient (e.g., > 0.90) indicates a homogeneous test. However, like Cronbach's α, homogeneity (that is, unidimensionality) is actually an assumption, not a conclusion, of reliability coefficients.
In a sample of participants with bipolar disorder, the cronbach's alpha was 91. [1] Additionally, it has the ability to accurately differentiate pediatric bipolar disorder from ADHD and healthy controls greater than 90% of the time. The teacher version (CMRS-T) also has 21 items. The internal consistency, measured by Cronbach's alpha, was .86. [3]