Register June 2004 No. 582
APPENDIX A
Regression Formula for Calculating Significant Discrepancy Scores
Information needed for Calculation:
IQ/Ability Score = SD of IQ/Cognitive Test = (SDi)
Achievement Score = SD of Achievement Test = (SDa)
Correlation between tests = 0. (r)*
Formula:
Expected Achievement = (SDa/SDi)r(IQ-100)+100 = ______ Discrepancy = Expected Achievement - Obtained Achievement Score =
Discrepancy / SD Discrepancy =
If number is greater than 1.75, there is a significant discrepancy between achievement and ability scores
* If correlation between tests is unknown, use .62
When the test publisher provides tables for significant differences between ability and achievement scores (such as with the Weschler Intelligence Scale for Children- 3 and the Weschler Individual Achievement Test), these tables may be used in lieu of this formula. Cut-offs should be derived using a 1.75 Standard Error of Estimate (SEe) criterion so that the difference between expected and obtained scores in the bottom 4% of the distribution meet the standard for a significant discrepancy (i.e. 1.75 SEe units below the expected score).
