[Rasch] Rasch to G-theory
rmt at rasch.org
Tue Apr 10 16:43:51 EST 2012
The variances needed to compute a Rasch-based equivalent to a
Generalizability Coefficient (G) are in Facets Tables 5 and 7.
My apologies that the "explained variance" computations at
www.winsteps.com/facetman/table5.htm do not show the last step in the
computation. It is:
G = (Explained variance% by target facet) / 100
Please verify this value of G makes sense for your data. A more specific
Generalizability Coefficient may be more meaningful to your audience.
Variance terms similar to
page 20 can be extracted from Facets output. These can be used to compute a
more focused Generalizability Coefficient.
At 4/10/2012, you wrote:
>can anyone direct me to a paper which explains how to use Rasch measured
>reported by Facets to compare the results with G-theory estimates? For
>example, I can read in the Facets output the sd of item measures, the sd
>of rater measures and the sd of person measures. How can I produce an
>index which is similar to the variance attributed to markers as computed
>in generalizability theory? Or maybe this is not possible? A good search
>on the internet did not help me a lot, although I reached a paper by
>Macmillan (2000) which, unfortunately, I cannot have access.
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT: 25:4 Spring 2012
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