Confidence intervals for test scores and significance tests for test score differences: a comparison of methods.

Two methods of setting confidence intervals for test scores and testing the significance of test score differences are compared with respect to their simplicity and the similarity of their results. The conventional method, which is based on obtained scores, is unquestionably simpler than the technically correct method, which is based on estimated true scores, but the two methods may give rather different results, depending on the reliability coefficient(s) of the test(s), the distance of the score(s) from the mean, and the confidence or significance level. The standardization data for the WISC-R are used to illustrate the effects of those factors.