| 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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Showing posts with label composite scores. Show all posts
Showing posts with label composite scores. Show all posts
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, September 24, 2015
WISC-V expanded index scores: Verbal Expanded Crystallized (Gc) and Expanded Fluid (Gf) index scores and tables
Click on image to enlarge for easier reading
Somehow I seemed to have missed this development on my research literature monitoring radar. More comments and a link to the technical report can be found at Joel Schneider's excellent blog.
Friday, January 13, 2012
How to estimate best IQ score if someone has taken multiple IQ tests: The psychometric magic of Dr. Joel Schneider
Dr. Joel Schneider has posted an excellent explanation on how to estimate a person's "true IQ score" when a person has taken multiple IQ tests at different times. Probably the most important take-away message is one should never calculated the simple arithmetic average. The median would be more appropriate, but Joel provides and even more psychometrically sound method and an Excel spreadhsheet for implementing his excellent logic and methods.
- Posted using BlogPress from Kevin McGrew's iPad
- Posted using BlogPress from Kevin McGrew's iPad
Thursday, March 31, 2011
Why IQ composite scores often are higher or lower than the subtest scores: Awesome video explanation
This past week Dr. Joel Schneider and I released a paper called " 'Just say no' to averaging IQ subtest scores." The report generated considerable discussion on a number of professional listservs.
One small portion of the paper explained why composite/cluster scores from IQ tests often are higher (or lower) than the arithmetic mean of the tests that comprise the composite. This observation often baffles test users.
I would urge those who have ponder this question to read that section of the report. And THEN, be prepared to be blown away by an instructional video Joel posted at his blog where he leads you through a visual-graphic explanation of the phenomena. Don't be scared by the geometry or some of the terms. Just sit back and relax and now recognize, even if all the technical stuff is not your cup-of-tea, that there is an explanation for this score phenomena. And when colleagues ask, just refer them to Joel's blog.
It is brilliant and worth a view, even if you are not a quantitatively oriented thinker.
Below is a screen capture of the start [double click on icon to enlarge]
- iPost using BlogPress from my Kevin McGrew's iPad
One small portion of the paper explained why composite/cluster scores from IQ tests often are higher (or lower) than the arithmetic mean of the tests that comprise the composite. This observation often baffles test users.
I would urge those who have ponder this question to read that section of the report. And THEN, be prepared to be blown away by an instructional video Joel posted at his blog where he leads you through a visual-graphic explanation of the phenomena. Don't be scared by the geometry or some of the terms. Just sit back and relax and now recognize, even if all the technical stuff is not your cup-of-tea, that there is an explanation for this score phenomena. And when colleagues ask, just refer them to Joel's blog.
It is brilliant and worth a view, even if you are not a quantitatively oriented thinker.
Below is a screen capture of the start [double click on icon to enlarge]
- iPost using BlogPress from my Kevin McGrew's iPad
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