[Rasch] Items with various partial credit models

Ricardo Primi rprimi at uol.com.br
Fri Jun 16 14:17:54 EST 2006


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 estimated under Scheme 2. The item
in and outfit measures are also a bit higher under Scheme 2. So the Scheme 1
appears to be better but I 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 in 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? 

Thank you 

Ricardo Primi

Universidade São Francisco
Graduate Program in Psychology
Rua Alexandre Rodrigues Barbosa, 45
Itatiba, São Paulo, Brazil
E-mail rprimi at uol.com.br


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