Definition
Reliability coefficient is an index of the amount of true variance operating in a set of raw test scores (Aron & Aron, 2003).
Description
The reliability coefficient is represented by the term r xx , the correlation of a test with itself. Reliability coefficients are variance estimates, meaning that the coefficient denotes the amount of true score variance. This is unlike a standard correlation coefficient where, usually, the coefficient needs to be squared in order to obtain a variance (Cohen & Swerdlik, 2005).
To estimate test-score reliability, at a minimum, one needs at least two observations (scores) on the same set of individuals. The correlation between the sets of observations provides a reliability coefficient. From this simple requirement, a wide variety of reliability studies could be designed, such as the test-retest reliability, the internal-consistency...
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References
Allen, M. J., & Yen, W. M. (2002). Introduction to measurement theory. Long Grove, IL: Waveland Press.
Aron, A., & Aron, E. N. (2003). Statistics for psychology (3rd ed.). Upper Saddle River, NJ: Prentice Hall.
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Piedmont, R.L. (2014). Reliability Coefficient. In: Michalos, A.C. (eds) Encyclopedia of Quality of Life and Well-Being Research. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-0753-5_2463
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