[Rasch] A basic question about variance calculations
mike at winsteps.com
Tue Aug 20 14:09:44 EST 2013
Thank you for your questions, Imogene.
Explained variance % by facet 1 = (Explained variance %) * v1 /vsum
Explained variance % = Variance explained by Rasch measures of all
facets / Total variance in the data
= (Score Population S.D.^2 - Resid^2) / (Score Population S.D.^2)
v1/vsum = Rasch variance explained by facet 1 / Total Rasch variance
explained by all facets
= (measure S.D. facet 1)^2 / sum ( (measure S.D. facet 1)^2 +
(measure S.D. facet 2)^2 + ... )
so that, "Explained variance % by facet 1 " is the % of the total
variance in the data explained by facet 1.
On 8/19/2013 17:32 PM, Imogene Rothnie wrote:
> Dear All
> I've been calculating the variance explained after a Facets analysis
> using the information from table 5 and 7 output in Facets and the
> formulas provided in the Help menu. A basic question: when we
> calculate a % variance explained for a facet, say Judge, is the a % of
> the 'variance explained ' total ? Or is it variance explained /100% ?
> (ie 100% including the residual error). Hence 40% variance explained
> by Judges when 50% variance explained by the measures would be 20%
> variance explained of total in the former...?
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