[Rasch] Re: Urgent question

iasonas lambrianou liasonas at lycos.com
Sun Jan 29 04:19:48 EST 2006

Dear friends,
I have a very urgent question, anyone who can contribute, please do so

We use the t-scores (z scores) of the examinees on high stakes tests to sort them according to their ability. 
When the distribution of the raw scores deviates a lot from the normal, then the t-scores look a bit 'strange'. Do you also agree that t-scores can not be used when the distribution deviates substantially from the normal?
Also, I can transform the raw scores using y=ln(x/(100-x)) and the distribution of the raw scores becomes normal. Then, I can get more 'beautiful' t scores (z scores). Am I allowed to use this transformation and then get the t scores?



> ----- Original Message -----
> From: "Mike Linacre (RMT)" <rmt at rasch.org>
> To: rasch at acer.edu.au
> Subject: [Rasch] Different models: counts to scale conversion
> Date: Mon, 23 Jan 2006 14:58:51 -0600
> Not sure about the contrast "log-scaled" vs. "Rasch-scaled"
> Georg Rasch based his theory on the Poisson model, which is a Rasch 
> model and is a log-scaling model. It seems the actual contrast is 
> between a Rasch-Poisson model and a Rasch rating-scale-type model.
> Mike L.
> Earlier remark:
> > When I was predicting the amount of money that a counselor was 
> > going to be sued for a bad outcome based the hierarchical 
> > complexity of the informed consent procedure. Log money did the 
> > best.  Right behind it by just a little worse .96 versus .94 was 
> > Rasch scaled money.  The value of money has been argued to 
> > require loging for years.
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> Rasch at acer.edu.au
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Dr. Iasonas Lamprianou
CFAS, School of Education
The University of Manchester
Oxford Road, Manchester M13 9PL, UK
Tel. 0044  161 275 3485
iasonas.lamprianou at man.ac.uk


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