Forrest Gump and IQ Expectations

A Lesson from Forrest Gump Regarding Expectations for Students with Cognitive Disabilities

Kevin S. McGrew, PhD

Director

Institute for Applied

Psychometrics (IAP) llc

Visiting Professor

Educational Psychology

University of Minnesota

www.iapsych.com

Mrs. Gump: Well, we're all different, Mr. Hancock. He might be a bit on the slow side. He's not going to a special school to retread tires ! Principal: Your boy's... different, Miz Gump. His IQ's 75.

As we all know, Forrest accomplished a lot --- much more than his IQ score would have suggested. How can this be ? “ Sometimes there just aren’t enough rocks”

Lets get an empirical answer from a national norm sample – the Woodcock-Johnson Battery-Third Edition (Woodcock, McGrew & Mather, 2001; WJ III) What should our expectations be for Forrest in reading?

What should our expectations be for Forrest in reading? 40 50 60 70 80 90 100 110 120 130 140 150 160 IQ=75 + 5 Forrest Gump’s score

WJ III GIA SS 70-80 (in the norm data) What should our expectations be for Forrest in reading? 40 50 60 70 80 90 100 110 120 130 140

Ability/Achievement Relations – Reuire Adjusting for “Regression to the Mean ” This model reflects the less than perfect correlation between ability and achievement measures Ability Achievement 100 115 130 85 70 100 115 130 85 70

90 100 110 120 130 140 40 50 60 70 80 Expected Basic Rdg Skills SS (for GIA SS = 70-80 ) ???? WJ III GIA SS 70-80 (in the norm data ) Must first account for “ regression to the mean ”

90 100 110 120 130 140 BRS 40 50 60 70 80 Basic Rdg Skills SS (for GIA SS = 70-80 ) Where will most of the Forrest Gumps of the world achieve in reading? Regression-based expected score

Intelligence tests: Quantoid fact 1

For any given IQ score:

Half of the students will obtain achievement scores at or below their IQ score.

Half of the students will obtain achievement scores at or above their IQ score !

IQ test scores, under optimal test conditions, account for 40 % to 50% of current expected achievement

Thus, 50% to 60 % of student achievement is related to variables “ beyond intelligence ”

Intelligence tests: Quantoid fact 2

The relationship between intelligence and achievement in a nationally representative sample – these are REAL subjects WJ III Battery norm data (see McGrew & Woodcock, 2001) WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75 Note the normal curve shape of both the IQ and Ach distributions

The relationship between intelligence and achievement in a nationally representative sample – these are REAL subjects The “tighter” the spread of the individual data points (ideally along a single line cutting through the middle of the plot) the more accurate the prediction of achievement will be based on IQ. The amount of spread around the line represents the amount of error when trying to make a prediction based on IQ. Technically it is called the standard error of estimate . WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75

WJ III General Intellectual Ability WJ III Total Achievement IQ-ACH correlation = .75

Lets pull a slice of the data points out for closer inspection.

Lets select all subjects with IQ scores between 70 and 80.

What will their achievement scores look like?

Will their achievement scores be < 80?

The WJ III Total Achievement scores for WJ III norm subjects with IQ (GIA) scores from 70-80 Lets rotate/flip this figure 90 degrees WJ III General Intellectual Ability WJ III Total Achievement

The WJ III Total Achievement scores for WJ III norm subjects with IQ (GIA) scores from 70-80 WJ III General Intellectual Ability WJ III Total Achievement IQ range = 70-80 ACH range = 44-110

Half the subjects with IQs from 70-80 are achieving below the predicted or expected level based on IQ score

Half the subjects with IQs from 70-80 are achieving above the predicted or expected level based on IQ score

Does this finding happen at all IQ levels?

WJ III General Intellectual Ability WJ III Total Achievement IQ range = 60-70 ACH range = 43-94 The WJ III Total Achievement scores for WJ III norm subjects with IQ (GIA) scores from 60-70 YES

The WJ III Total Achievement scores for WJ III norm subjects with IQ (GIA) scores from 70-80 WJ III General Intellectual Ability WJ III Total Achievement ACH range = 44-110 IQ range = 70-80 ACH range = 44-110 It is important to remember that these are not abstract data points. These are REAL children with the same general level of cognitive abilities.

Evan a high IQ score is no guarantee of success

Can we predict 1 year gain with any reasonable degree of accuracy?

WJ III Norm test-rest sample (n=415+)

Grades 0.1 to 12.9

Retest interval

3 to 31 months

Mean = 14.6 months

SD=3.5 months

Change scores rescaled to 1 year gain (AYP)

Pretest predictors in multiple regression model

Age

Grade

Initial achievement score

General Intellectual Ability (GIA) score - g

AYP

Can we predict 1 year gain with any reasonable degree of accuracy? WJ III Ach cluster R R 2 SEM (in SD units) Basic Rdg Skills .75 .57 + .57 SD Reading Comp .70 .49 + .67 SD Math Calc .52 .27 + .84 SD Math Reasoning .51 .26 + 1.00 SD AYP We can account for (predict) approximately ½ of the AYP In reading and approximately ¼ in math for individual students

Intelligence tests are fallible predictors of current and future achievement At best, typical IQ-Ach correlations are in the .60 to .70+ range IQ ACH Our IQ tests can only account for 35% to 50% of school achievement

Current research and assessment technology does not allow us to accurately predict which individual children will be at a specified level of proficiency/mastery at any given time

(e.g., who will be in the top half of the achievement distribution for a given level of general intelligence)

For most children with cognitive disabilities (those with below average IQ scores), it is NOT possible to predict individual levels of expected achievement, or AYP with the degree of accuracy that would be required to deny a child the right to challenging standards and expectations