[Rasch] Reliability in the Rasch methodology
Mike Linacre (RMT)
rmt at rasch.org
Sun Jun 15 05:10:15 EST 2008
Thank you for your question.
>In the Rasch world, what is the interpretation for the (a) person
>reliability, and (b) item reliability?
"Reliability" in both Rasch theory and Classical Test Theory is the
statistical reproducibility of a set of values (Rasch measures or raw
scores). It is the hypothesized "true" variance of those values divided by
their observed variance. CTT computes this for the raw scores of the
current sample of persons and reports it as the "test reliability". Rasch
computes it for the Rasch measures (abilities) of the current sample of
persons (the "person" reliability) and the Rasch measures (difficulties) of
the current sample of items (the "item reliability").
There is a comparison of Rasch person reliability and CTT test reliability
Editor, Rasch Measurement Transactions
rmt at rasch.org www.rasch.org/rmt/ Latest RMT: 21:4 Spring 2008
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