Threshold values for significant changes in test-retest difference scores for the Wechsler Intelligence Scale for Children – Fourth Edition

One of the purposes of administering intelligence scales is to assess changes in cognitive functioning over time, from a few days to several years, to determine whether the examinee has progressed or regressed after treatment or other events. (e.g., an accident, a rehabilitation, etc.). The present research aimed to study the short term practice effect of the Wechsler Intelligence Scales for Children – Fourth Edition and provide threshold values that allow practitioners to assess whether there are true differences in individual performance or whether these differences are due to chance. A sample of 440 subjects was administered the WISC-IV twice with an average interval of 30 days. The results show that practice is more pronounced when using raw subtest scores than when using weighted scores. Threshold values for assessing significant change in subtests and indices were obtained. For example, for the Full-Scale Intelligence Quotient, a difference between 6 and 27 IQ points between the first and second administration indicates a practice effect. Conversely, if the difference is equal to or less than 5 IQ points, then there was a decline, while if it is equal to or greater than 28 IQ points, there was an increase in performance not due to the practice effect. Therefore, these data should allow practitioners to more accurately assess the clinical significance of observed changes during a short term dual administration.