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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]
For the reliability of a two-item test, the formula is more appropriate than Cronbach's alpha (used in this way, the Spearman-Brown formula is also called "standardized Cronbach's alpha", as it is the same as Cronbach's alpha computed using the average item intercorrelation and unit-item variance, rather than the average item covariance and ...
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 average Cronbach's alpha is .71. It is available in 19 languages and has been used worldwide. Support materials for interpretation and training are available in each language.
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.
Internal consistency is the extent to which the items on a scale generally measure the same thing. Cronbach's alpha values (an estimate of internal consistency) median (average) values were 0.84 for the personality pattern scales, 0.83 for the clinical syndrome scales, and 0.80 for the Grossman Facet Scales. [1]
In testing validity of the IPI-2, internal consistency was measured using Cronbach's Alpha (overall=0.52). Significant correlations (<.05) were analyzed between IPI-2 scales and MMPI-2-RF and the PAI (Personality Assessment Inventory). Results are combined with Field Training Officer (FTO) Predictions, in order to provide a more complete analysis.