[Rasch] Items with various partial credit models

Mike Linacre (RMT) rmt at rasch.org
Fri Jun 16 14:29:35 EST 2006


Dear Ricardo:

Thank you for contacting us.

Your two schemes differ because of the Winsteps default of 
"STKEEP=YES".  If you want them to be the same, set "STKEEP=NO"

So, assuming you are using different GROUPS= indicators for the different 
item structures, then

For STKEEP= NO, IVALUEA="1114557"  means "1112334" with the categories 
treated as strictly ordinal.
For STKEEP=YES, IVALUEA="1114557"  means "1114557" with the unobserved 
intermediate categories 2, 3, 6 treated as sampling zeroes.

Please email me if you need more assistance.

Mike Linacre

At 6/16/2006, you wrote:
>Dear list members
>I am working with a personality test with 7 point rating scale items. But 
>I found that most items in fact work with 2 to 4 categories.
>The question that I have is about recoding. I tried two coding schemes:
>CODES = "1234567"
>Scheme 1:
>IVALUEA= "1112334"
>IVALUEC= "1112223"
>IVALUEF= "1111222"
>IVALUEG= "1111223"
>Scheme 2
>IVALUEA= "1114557"
>IVALUEC= "1115557"
>IVALUEF= "1111777"
>IVALUEG= "1111447"
>I expected to come up with the same results but I found out that the two 
>subjects estimated measures using the two coding schemes are not perfectly 
>correlated. In high end the same theta under Scheme 1 is associated with 
>little spread of measures when they are am no sure about using this coding 
>scheme. My question is: I s there a rule in this cases? Is there a problem 
>with the fact that i[Rasch] Items with various part.ems n some items the 
>maximum item score would be 4 while in other items would be 2, that is, 
>with the fact that they don s have the same maximum?
>Ricardo Primi

Mike Linacre
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT: 19:4 Spring


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