[Rasch] I have about 80 items on depression and anxiety for which I have about 100 participants.
ici_kalt at yahoo.com
Tue Sep 21 00:05:28 EST 2010
If the purpose is to have a screening test to detect anxiety (and another screen for depression), then you should look at the "critical" items representing the traits of anxiety.
As a first approach probably you do not need to have items uniformly distributed along the complete scale. To choose the critical items you may (a) ask the experts to choose the more representative set, (b) make a comparison among two groups of people showing anxiety and not showing anxiety according to the experts, (c) find the cut off point where a difference is obtained between both groups of persons.
A second approach can be done looking for those items where persons with anxiety show a misfit. It could happen that those items able to detect a misfit on problematic patients could be the best suitable to be used for screening, while well behaved items on infit and outfit may be useful to get measures on a complete test for detailed analysis.
hope this helps
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--- On Sun, 9/19/10, Michael Lamport Commons <commons at tiac.net> wrote:
From: Michael Lamport Commons <commons at tiac.net>
Subject: [Rasch] I have about 80 items on depression and anxiety for which I have about 100 participants.
To: Rasch at acer.edu.au
Date: Sunday, September 19, 2010, 11:33 PM
I have about 80 items on depression and anxiety for which I have about 100 participants. I would like to choose a minimal set of items to test for depression and possibly on a separate scale for anxiety. I plan to factor the results and then do a Rasch on each dimensions separately. Is the way to choose the best items -- the ones that have the least variability in difficulty.-- is to choose roughly equally spaced items with low in-fit and outfit scores, or what? We could get more participants
Michael Lamport Commons, Ph.D.
Assistant Clinical Professor
Department of Psychiatry
Harvard Medical School
Beth Israel Deaconess Medical Center
234 Huron Avenue
Cambridge, MA 02138-1328
Telephone (617) 497-5270
Facsimile (617) 491-5270
Cellular (617) 320–0896
Commons at tiac.net
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