Reliability refers to the consistency or repeatability of measurement. It is defined as the extent to which the variance of an observed variable is explained by the true score that the variable is designed to measure. In other words, the reliability is defined as the ratio of the true score variance to the total variance of the observed measure. Let us define where is the true score that y is to measure and is the measurement error. The reliability of variable y is defined as the ratio of variance explained by the true score to the variance to the observed variance of y:

where and are variance of the true score and variance of measurement error; respectively, and is the factor loading. Note that the reliability defined in Equation (2.10) is in fact ...

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