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:

- See PDF for diagram Expected Achievement = (SDa/SDi)r(IQ-100)+100 = ______

Discrepancy = Expected Achievement - Obtained Achievement Score       =

- See PDF for diagram - See PDF for diagram SD Discrepancy = SDa √ 1-r 2                 =

- See PDF for diagram Cut-off:

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).