[Rasch] Rasch model affected by item type or not

iasonas liasonas at cytanet.com.cy
Fri Mar 12 05:37:32 EST 2010

i agree with Rense, but just a friendly word of caution.
If by item "type" you mean the format of the item i.e. multiple choice or
short response, then in many cases this may affect the results a little bit
because the item may tap on a slightly different dimension. I am trying to
say that what Rense suggests happens only the model-data fit is practically
satisfactory; otherwise, invariance does not hold
thank you


From: rasch-bounces at acer.edu.au [mailto:rasch-bounces at acer.edu.au] On Behalf
Of Rense Lange
Sent: Thursday, March 11, 2010 7:32 PM
To: Parisa Daftari Fard; Rasch at acer.edu.au
Subject: Re: [Rasch] Rasch model affected by item type or not

Item later in the test tend to be affected due to fatigue, running out of
time, etc. and short tests are more sensitive to changes in items. But,
other than that, items won't change their relative locations regardless what
else is in the test. There may be random error. Just take any Rasch data
set, calibrate all items, then rerun with some items removed. Unless very
few items remain, a scatter plot of the non-removed items in these two cases
will parallel Y=X.

On 3/10/10, Parisa Daftari Fard <pdaftaryfard at yahoo.com> wrote: 

Dear Rasch list members,
I came up with a question and I hope to have your reply. Does test
configuration (the ordering of the item types and the adding or subtracting
the item types) affect Rasch outcome in terms of the hierarchical order in
item map? 
Does Rasch approach the item generically or pragmatically? by Generic I mean
that adding one item type (not the total number but the cognition related
item type) would not affect the pattern of items because the statistics is
doing something on the nature of the item.
I am not sure if I am clear?

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Rense Lange, Ph.D.
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