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 .

A measure of experimental error. Variance arising from unrecognized or uncontrolled factors in an experiment with which the variance of unrecognized factors is compared in tests of significance.

The scores on a variable can vary between participants. When this variance is not ude to the independent variable it is error variance, and is a source of unreliable variation that cannot be explained. Error variance can be due to measurement errors, the method of data collection, and so on.