Definitions for

**"Error variance"**Variability in the value of the dependent variable that is related to extraneous variables and not to the variability in the independent variable.

In the true score model, the component of variance attributable to random sources irrelevant to the trait or ability the test purports to measure in an observed score or distribution of scores. Common sources of error variance include those related to test construction (including item or content sampling), test administration, and test scoring and interpretation, 18, 129

unreliable and inexplicable variation in a variable. Error variance is assumed to be independent of common variance, and a component of the unique variance of a variable. See common variance , unique variance and specific variance .