This study examined the reliability of three methods for detecting differential item functioning (DIF) (i.e., the Mantel-Haenszel method, the standardization method, and the logistic regression method) applied to achievement test data. In addition, the study examined the influences of different sources of error variance, including examinee, occasion, and curriculum sampling on the magnitude of the reliability of the different DIF detection methods. Three datasets were assembled from the 1992 spring and fall standardization administration of the Iowa Tests of Basic Skills, and these were manipulated to control for error variance sources. Results indicated that the Mantel-Haenszel and standardization methods were more reliable in detecting DIF than the logistic regression method. The data also indicated that controlling the error variance of curriculum sampling slightly increased the reliability of DIF detection while controlling for error variance due to examinee sampling gives confusing results. (Contains 13 tables, 8 figures, and 12 references.) (Author/SLD)