[Rasch] Explained variance

Michael Lamport Commons commons at tiac.net
Tue Oct 21 07:29:26 EST 2008

For hierarchical complexity and Rasch Score, the r2 are .8 or higher for the moral, social, social perspective taking, political domains, and .9 or above in math, physics, chemistry, and logic.  We share your opinion about the low r's.  Assessments are messier than instruments so r2 of .75 to .80 are very good.


-----Original Message-----
>From: Theo Dawson <theo at devtestservice.com>
>Sent: Oct 20, 2008 8:55 AM
>To: Rasch Mailing List <Rasch at acer.edu.au>
>Subject: [Rasch] Explained variance
>Are there any established standards for the percentage of variance we  
>would like to see explained by the Rasch measure? Our cognitive  
>developmental assessments run 70%-80%, but for conventional tests we  
>have worked with the value is often lower than 30%.
>Also, for multiple choice tests, would it be typical for the first  
>factor from the residuals to have something to do with guessing?
>Take the Sort Task Challenge at:  http://devtestservice.com/sorttasklead.php
>Theo Linda Dawson, Ph.D.
>President & CEO, Developmental Testing Service, LLC (DTS)
>Northampton, MA 01060
>theo at devtestservice.com
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>At the Developmental Testing Service, LLC (DTS), we are dedicated to  
>developing assessments that capture the transformations in thinking  
>that occur up to 13 times over the course of the lifespan. Each of  
>these transformations leads to a more complex, integrated, and  
>adequate way of thinking. Whereas traditional tests examine what  
>people know, our tests examine how they think about what they know.
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My best,

Michael Lamport Commons, Ph.D.

Assistant Clinical Professor
Department of Psychiatry
Harvard Medical School

Program in Psychiatry and the Law
Beth Israel Deaconess Medical Center
commons at tiac.net

617-497-5270 Telephone
617-491-5270 Fax

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