Stability of intelligence from infancy through adolescence

Stability of intelligence from infancy through adolescence: An autoregressive latent variable model (article link)

Huihui Yua, D. Betsy McCoach, Allen W. Gottfriedc, Adele Eskeles Gottfriedd

a Yale University, United States b University of Connecticut, United States c Fullerton Longitudinal Study, California State University, Fullerton, United States d California State University, Northridge, United States

A B S T R A C T

This study examined the stability of the latent construct of intelligence from infancy through adolescence, using latent variable modeling to account for measurement error. Based on the Fullerton Longitudinal Study data, the present study modeled general intelligence across four developmental periods from infancy through adolescence. The Fullerton Longitudinal Study included twelve assessments of intellectual performance over a sixteen-year interval. Three assessments of intellectual performance at each of four developmental periods served as in-dicators of latent intelligence during infancy (1, 1.5, and 2 years old), preschool (2.5, 3, and 3.5 years old), childhood (6, 7, and 8 years old), and adolescence (12, 15, and 17 years old). Intelligence exhibited a high degree of stability across the four developmental periods. For instance, infant intelligence revealed a strong cross-time correlation with preschool intelligence (r = 0.91) and moderate correlations with childhood and adolescent intelligence (r = 0.69 and 0.57, respectively). Intelligence followed a stage-autoregressive pattern whereby correlations between IQ scores decreased as the timespan between assessment waves increased. Further, from infancy to adolescence, the effect of intelligence during earlier periods was completely mediated by intelligence during the adjacent developmental period. In contrast to much prior research, this study demonstrated the stability of general intelligence, beginning in infancy.

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Law Review Article: Maroney (2011) on Adolescent Brain Science since Graham v FL

The following has been added to the ICDP Law Review Article blogroll.

Maroney, T. A. (2011). ADOLESCENT BRAIN SCIENCE AFTER GRAHAM V. FLORIDA. Notre Dame Law Review, 86(2), 765-793.


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Court Fails To Bite on Defense Chicanery (Guest post): Atkins MR/ID decsions--Meyers v AL (2011)

A recent Atkins MR/ID decision re: Myers v Allen (AL; 2011, 2009, 2007) has been posted to the ICDP Court Decision blogroll. In addition, regular ICDP contributor, Kevin Foley, has provided the following guest blog commentary.


Court Fails To Bite on Defense Chicanery - Guest post by Kevin Foley.



Alabama inmate Robin Myers’ federal habeas attorneys claimed that Myers was mentally retarded (intellectually disabled). Myers had a big problem – his most current IQ testing on the WAIS-III, administered in 2006 - a year or so before his hearing when he was about 45 years old - showed a valid full scale IQ score of 84. Under most current definitions of intellectual disability, such a score sounds the death knell for an Atkins claim, since a person must prove that he currently intellectually disabled, and that he has scores which satisfy the first prong of the diagnosis. If the Flynn Effect was applied to his score, the most Myers could gain would be about 3 points, meaning his level of intellectual functioning would still be an 81, outside the range for a diagnosis of intellectual disability.

​Since Myers had some full scale IQ scores when he was a child that were in the intellectual disability range (75, 74, 71, and 64), his attorneys argued that what was relevant to the claim was whether Myers was intellectually disabled before age 18. The defense expert, “testified . . . that he was asked only to form and express an opinion about petitioner’s mental capacity before the age of 18, not his current capacity or his capacity at the time of the murder.” The court rejected the ploy, concluding that, “it is clear that Alabama courts would find that evidence of an IQ below 70 as a child, absent additional evidence of similar current scores and current deficits in adaptive skills, is not sufficient to render a defendant exempt from the death penalty. The Alabama Supreme Court specifically noted that ‘focus on [the defendant’s] functioning before the age of 18 is misplaced’ when that defendant’s ‘intellectual functioning and behavior as an adult places him above the mentally [retarded] range.’”

​The court was also unimpressed with the defense expert’s attempt to explain the 20 point increase in IQ score from childhood to adult (the expert contended that the childhood IQ score of 64 to be “the most accurate and complete’). According to the magistrate judge’s opinion, the defense expert “further explained the improvement in Mr. Myers’ IQ scores as a result of brain injury”. Of course, one typically associates a brain injury with a potential decline in intellectual functioning, not a gain. But the expert’s proffered explanation was of no consequence to the court, which pointed out that notwithstanding this explanation, the expert, “does not consider [Myers] to be mentally retarded at the present time.”


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Court Decision: Smith v TN (2010)

Still "cleanin' out my in box."

The Tennessee Court of Criminal Appeals rendered a very interesting (perplexing?) ruling recently. I only had time for a quick skim. With that caveat, the decision for Leonard Smith is available here. I will add it to the ICDP Court Decisions blog roll in the next day or so. Thanks again to the ever diligent Kevin Foley for sending this one my way.

Of interest is how the post conviction relief court dealt with a large number of IQ scores from ages 14 thru adulthood---tests that varied from comprehensive intelligence batteries to tests that were quick and limited screening instruments. Present in the document are the following scores. Those based on a comprehensive intellectual battery are designated by asterisks

1975 WISC 80*
1975 Ammons Quick Test 70
1976 Ammons Quick Test 84
1980 Un-named (prison) 88
1984 PPVT 86
1989 WAIS-R 75*
2001 WAIS-III 77*
2002 WAIS- III 65*


One troubling statement is on page 51:

“Specifically, the post-conviction court rejected the IQ scores achieved by [Smith] during his adult years and, apparently referencing the performance IQ achieved in 1975 when he was fourteen years of age, concluded that ‘testing preformed before the ate of eighteen reflects a functional I.Q. of 85.’”

Although there are individual cases were a component or sub-score index score may be the best estimate of a person's general level of intellectual functioning, in general, the overall "full scale" IQ should always be given first priority consideration in Atkins cases. I am baffled that given four different Wechsler Full Scale IQ scores a decision was made to "cherry pick" the Performance Scale IQ of 85 from the WISC administered when Smith was a teenager. How can all the adult scores simply be dismissd without an explanation?

In addition, the appeals court rejected the concepts of the standard error of measurement (SEM) and norm obsolescence (aka, the Flynn Effect) and stuck with the states supreme court and acknowledged, that by taking this approach, persons with MR/ID will be executed in Tennessee. Hmmmm? Atkins claim denied.

In the end, though, Smith got some relief based on his trial attorneys failure to get a judge recused.

Strange twists and turns.

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