[Rasch] Investigating Dimensionality
Mike Linacre (RMT)
rmt at rasch.org
Wed Jul 21 15:00:28 EST 2010
Thank you for your question, Jacob.
Yes, you can split the items into two subsets based on their loadings on
contrast (component, factor), and compare the person abilities on the two
sets of items.
1. Put a code into the item label to indicate the subset to which the item
2a. Use ISELECT= for each subset code, and produce a person measure
(PFILE=). Cross-plot the person measures.
2b. Do a Differential Person Functioning (DPF=) analysis based on the
subset code. Table 31.1 will give you an inter-item-subset t-test for each
mike at winsteps.com
At 7/20/2010, you wrote:
>I'm interested in investigating dimensionality in a data set and see many
>references to E.V. Smith's (2002) paper in the Journal of Applied
>Measurement on this topic. It appears that RUMM2030 has a standard routine
>to do this analysis, but I'm unsure if the analysis can be done in
>Winsteps. As an alternative, could one split items into subtests based on
>the positive and negative loadings on a particular contrast and compare
>the item difficulties for those two sets?
>Any input is appreciated.
>Jacob Kean PhD
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