Friday, May 25, 2018

Does IQ predict future achievement in reading, writing and math?


Watkins, M. W., Lei, P. W., & Canivez, G. L. (2007). Psychometric intelligence and achievement: A cross-lagged panel analysis. Intelligence35(1), 59-68.  http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.397.3155&rep=rep1&type=pdf

 Fletcher and Miciak (2017) claim that "there is substantial evidence showing little difference between IQ-discrepant and low achieving children in achievement, behavior, or cognitive skills, prognosis, intervention outcomes, and neuroimaging markers of brain function".

IQ-DISCREPANT are children who have a discrepancy between their IQ score and their reading/writing/ math scores. The term IQ-DISCREPANT usually refers to children with poor reading/writing/math and (at least) average intelligence.  LOW ACHIEVING in Fletcher and Miciak's paper refers to children who have poor reading/writing/math and lower than average IQ scores.   These children do not have a discrepancy between their IQ and achievement scores.

Assertions like Fletcher and Miciak's were one of the reasons for abandoning the discrepancy definition of learning disability (learning disability as a discrepancy
between at least average IQ and poor reading/writing/math that cannot be explained by exclusionary factors) in DSM5.

This article by Watkins, Lei  & Canivez presents a slightly different picture:

In current usage, intelligence tests are thought to measure general reasoning skills that are predictive of academic achievement. Indeed, concurrent IQ–achievement correlations are substantial and, consequently, comparisons of IQ and achievement scores constitute one of the primary methods of diagnosing learning disabilities (at least when this paper was written). However, intelligence tests often contain items
 or tasks that appear to access information that is taught in school (i.e., vocabulary, arithmetic) and there has been considerable debate regarding the separateness or
 distinctiveness of intelligence and academic achievement.  This apparent overlap in test coverage, among other factors, has led some to view intelligence and achievement as identical constructs. Some researchers have suggested that the relationship between intelligence test scores and educational achievement is reciprocal, mutually influencing each otherAccording to this approach, children who read a lot develop their cognitive abilities and intelligence.  Children who do not read because of learning disabilities have less opportunity to develop these abilities.  Subsequently, special education researchers have suggested that only achievement tests should be used to identify children with learning  disabilities (as Fletcher suggests).  Other researchers assert that intelligence is causally related to achievement.

In order to determine whether and to what extent IQ affects achievement (or vice versa), children must be tested twice with an IQ test and twice with achievement tests over a period of a few years. If IQ affects achievement and causes it, the correlation between the IQ scores obtained in the first measurement (IQ 1) and the achievement scores obtained in the second measurement (achievement 2) should be higher  than the correlation between the achievement scores obtained in the first measurement (achievement 1) and the  IQ scores obtained in the second easurement (IQ2).

Two thousand school psychologists were randomly selected from the National Association of School Psychologists membership roster and invited via mail to participate in this study by providing test scores and demographic data obtained
 from recent special education triennial reevaluations. Data were voluntarily submitted on 667 cases by 145 school psychologists from 33 states. Of these cases, 289 contained scores for the requisite eight WISC-III and four academic
achievement subtests.

Special education diagnosis upon initial evaluation included 68.2% learning disability, 8.0% emotional disability and 8.0% mental retardation.  The rest of the students received other diagnoses.  The mean age of students at first testing was 9.25 years and the mean age of students at second testing was 12.08.

Contemporary versions of the Woodcock–Johnson Tests of Achievement, Wechsler Individual Achievement Test, and Kaufman Test of Educational Achievement were used in more than 90% of the cases. In reading, all achievement tests included separate basic word reading and reading comprehension subtests. In math, separate calculation and reasoning subtests were available for all academic achievement instruments

Here are some interesting correlations I found in the second testing (which took place when the child had already spent about three years in special education):

Basic reading skills were correlated 0.56 with Information, 0.42 with Similarities, 0.49 with Vocabulary.

Reading comprehension was correlated 0.64 with Information, 0.54 with Similarities, 0.47 with Picture Arrangement, 0.50 with Block Design, 0.60 with Vocabulary, 0.50 with Comprehension subtest.

Mathematical calculations were correlated 0.62 with Information, 0.55 with Similarities, 0.52 with Picture  Arrangement, 0.53 with Block Design, 0.57 with Vocabulary and 0.55 with Comprehension.

Mathematical reasoning was correlated 0.70 with Information, 0.63 with Similarities, 0.52 with Picture Arrangement, 0.58 with Block Design, 0.67 with Vocabulary, 0.65 with Comprehension.

The relatively high correlation of Information and Vocabulary with all achievement tests stands out.

In the first testing (before the child entered special education) the highest correlations were found between those same IQ subtests and achievement tests, but correlations were generally lower. The reason for this is unclear to me and the   researchers do not explain it.

Another thing that stood out to me was that the mean of the group of children in the Verbal Comprehension and Perceptual Organization indices did not change between the first and the second testing. This may be an indication of the stability of intelligence.  On the other hand, this may mean that the intervention the children may have received in special education did not improve their crystallized knowledge.

Even more striking is the fact that the average scores in basic reading, reading comprehension, mathematical calculations, and mathematical reasoning have not changed during these two years and eight months. This means that the children did
not make progress in their skill level relative to the norm, but on the other hand, they also did not fall behind. Another interesting thing is that the children's average scores in the achievement domains were average (around 85), not lower.

Oh, Glutting, Watkins, Youngstrom, and McDermott (2004) demonstrated that both g (general intelligence) and Verbal Comprehension contributed to the prediction of academic achievement, although g was at least three times more  important than Verbal Comprehension.

In the present study, the average correlation between IQ1 and Achievement2 was 0.466 while the average correlation between Achievement1 and IQ2 was 0.398. This means that IQ predicts achievement, not the other way around.

IQ tests were built by Alfred Binet to measure (and predict) the ability of students to succeed at school. This basic feature of IQ tests has been empirically supported for more than 100 years and is also supported by this study.

The assertion that IQ predicts future achievement has been tested with students in regular education.  In this study, it was examined with special education students and has also been confirmed. Some researchers have suggested that correlations between reading and IQ tests may often be an artifact of language, which affects both reading and intelligence.  By this line of thinking, reading difficulties lower
 IQ scores over time, and cause them to be weak predictors of achievement in students with learning disabilities.

One of the most influential researchers in the field of reading, Linda Siegel, wrote in 1998: “low scores on the IQ tests are a consequence, not a cause, of … reading disability”. I can find some logic in this argument, but I would mitigate it and say:
poor scores in some IQ subtests may also be caused by learning disability.

 The present study provides evidence that psychometric intelligence is predictive of future achievement whereas achievement is not predictive of future psychometric intelligence.

In conclusion, Fletcher and Miciak argue that there is no difference between children with and without an IQ-Achievement discrepancy in achievement, behavior,
 cognitive abilities, prognosis, intervention outcomes, and neuroimaging markers of brain function.

This study suggests that there is a difference in prognosis between these two groups of children.


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