[Rasch] Rating Scale or Partial Credit?
Mike Linacre (RMT)
rmt at rasch.org
Wed May 17 13:16:18 EST 2006
Thank you for your question. The literature is contradictory, so how about
The threshold distances can exaggerate differences between the item
structures. Rasch estimates are fairly robust against threshold variation.
So, instead, compare the model ICCs (expected score ogives). See the first
Figure on www.rasch.org/rmt/rmt151j.htm
If the differences are large enough to cause you to come to different
conclusions about the responses, then the rating scales are different and
the partial credit model is indicated. But check to make sure that there
are at least 10 responses in each category per item. Small category
frequencies can lead to idiosyncratic results.
At 5/16/2006, you wrote:
>I am analyzing data from a personality instrument that employs 5-option
>Likert-style items. Inspection of the results shows that the items vary
>greatly in terms of how well-spaced and well-ordered their thresholds
>are. Should I be using a partial credit model, because empirically I know
>the thresholds are different for each item? Or should I use a rating
>scale model, because the items were created with the intention of
>producing consistent thresholds?
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT: 19:4 Spring
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