Definition
Internal consistency reflects the extent to which items within an instrument measure various aspects of the same characteristic or construct.
Description
Internal consistency is a measure of reliability. Reliability refers to the extent to which a measure yields the same number or score each time it is administered, all other things being equal (Hays & Revicki, 2005). Classical test theory views an observed response as consisting of the sum of true score and error (Nunnally & Bernstein, 1994). True score for an individual is assumed to be invariant on repeated measurements. However, two parallel measurements will yield nonidentical observed scores as a result of random error of measurement. Because random errors are normally distributed, the true score will be located at the mean of the distribution of parallel measures. Observed scores actually include true score, systematic error, and random error components....
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References
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Hays, R., & Revicki, D. A. (2005). Reliability and validity (including responsiveness). In P. Fayers & R. Hays (Eds.), Assessing quality of life in clinical trials: Methods and practice (2nd ed., pp. 25–29). New York: Oxford University Press.
Nunnally, J. C., & Bernstein, I. C. (1994). Psychometric theory (3rd ed.). New York: McGraw-Hill.
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Revicki, D. (2014). Internal Consistency Reliability. 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_1494
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