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 .