| You must visit Joel Schneider's blog to see his awesome animations that help explain the composite score extremity effect. They are worth viewing, even if one does not understand them :) Click on wordpress.com and enjoy. |
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Wednesday, February 17, 2016
More on the Composite Score Extremity Effect: Awesome animations at Joel Schneiders blog
Tuesday, February 16, 2016
Why full scale IQ scores are often much lower (or higher) than the part scores? Dr. Joel Schneider on the "composite score extremity effect"
Bingo. There is finally an excellent, relatively brief, explanation of the phenomena of why full scale IQ scores often diverge markedly from the arithmetic average of the component index or subtest scores.
This composite score extremity effect (Schneider, 2016) has been well known by users of the WJ batteries. Why....because the WJ has placed the global IQ composite and the individual tests on the same scale (M=100; SD=15). In contrast, most other cognitive ability batteries (e.g., Wechslers) have the individual test scores on a different scale (M=10; SD=3). The use of different scales has hidden this statistical score effect from users. It has always been present. I have written about this many times. One can revisit my latest post on this issue here.
Now that the WISC-V measures a broader array of cognitive abilities (e.g., 5 index scores), users have been asking the same "why does the total IQ score not equal the average of the index scores?" Why? Because the five index scores are on the same scale as the full scale IQ score...and thus this composite score extremity effect is not hidden. A recent thread on the NASP Community Exchange provides examples of psychologists wondering about this funky test score issue (click here to read).
As per usual, Dr. Schneider has provided intuitive explanations of this score effect, and for those who want more, extremely well written technical explanations.
The WJ IV ASB 7 can be downloaded by clicking here. Although written in the context of the WJ IV, this ASB is relevant to all intelligence test batteries that provide a global IQ score that is the sum of part scores.
Kudos to Dr. Schneider.
This composite score extremity effect (Schneider, 2016) has been well known by users of the WJ batteries. Why....because the WJ has placed the global IQ composite and the individual tests on the same scale (M=100; SD=15). In contrast, most other cognitive ability batteries (e.g., Wechslers) have the individual test scores on a different scale (M=10; SD=3). The use of different scales has hidden this statistical score effect from users. It has always been present. I have written about this many times. One can revisit my latest post on this issue here.
Now that the WISC-V measures a broader array of cognitive abilities (e.g., 5 index scores), users have been asking the same "why does the total IQ score not equal the average of the index scores?" Why? Because the five index scores are on the same scale as the full scale IQ score...and thus this composite score extremity effect is not hidden. A recent thread on the NASP Community Exchange provides examples of psychologists wondering about this funky test score issue (click here to read).
As per usual, Dr. Schneider has provided intuitive explanations of this score effect, and for those who want more, extremely well written technical explanations.
The WJ IV ASB 7 can be downloaded by clicking here. Although written in the context of the WJ IV, this ASB is relevant to all intelligence test batteries that provide a global IQ score that is the sum of part scores.
Kudos to Dr. Schneider.
Click on image to enlarge
Thursday, February 4, 2016
Research Byte: The relations between CHC cognitive abilities and aspects of social support
Which aspects of social support are associated with which cognitive abilities for which people?
Abstract
Objectives.To assess the relations between 11 aspects of social support and five cognitive abilities (vocabulary, reasoning, spatial visualization, memory, and speed of processing) and to determine whether these relations between social support and cognition are moderated by age or sex.
Method.
A sample of 2,613 individuals between the ages of 18 and 99 years completed a battery of cognitive tests and a questionnaire assessing aspects of social support. A measure of general intelligence was computed using principal components analysis. Multiple regressions were used to evaluate whether each aspect of support and/or its interactions with age or sex predicted each cognitive ability and g.
Results.
Several aspects of social support were significantly related to all five cognitive abilities and to g. When g was included as a predictor, there were few relations with specific cognitive abilities. Age and sex did not moderate any of the relations.
Discussion.
These results suggest that contact with family and friends, emotional and informational support, anticipated support, and negative interactions are related to cognition, whereas satisfaction with and tangible support were not. In addition, these aspects of support were primarily related to g, with the exception of family contact. Social support– cognition relations are comparable across the life span and the sexes.
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