[Rasch] Fwd: Reliability, separation and strata
Fabio La Porta
fabiolaporta at mail.com
Wed Mar 1 19:07:52 AEDT 2017
I understand that 1) is the formula for the separation ratio (G), but I do
not understand the formulas for 2) and 3).
Are these related to the calculation of the reliability index starting from
H [(4G+1)/3 ?] and, respectively, the method suggested by Ben Wright for
skewed distributions in http://www.rasch.org/rmt/rmt144k.htm?
Also, the above method for skewed distributions allows to calculate G or H?
thanks for your reply.
2017-03-01 0:22 GMT+01:00 Mike Linacre <mike at winsteps.com>:
> There are three different Reliability/Separation/Strata options:
> 1. Spearman "Test" Reliability for the current sample -> Cronbach Alpha in
> CTT, and "Separation Reliability" for the observed person sample in Rasch.
> Separation ratio = square-root (Spearman Reliabity / (1-Spearman
> Reliability)). Normal distributions are assumed.
> 2. Strata for the current sample. This is the separation ratio, but with
> the tales of the observed person distribution treated as performance
> levels. Then "Strata reliability" = Strata^2 / ( 1+ Strata^2)
> 3. Wright's sample-independent method for strata. This shows the maximum
> number of statistically different strata the test can identify.
> Then "Wright Strata Reliability" = Wright Strata^2 / ( 1+ Wright
> Strata^2). This is the maximum possible value the "test" reliability.
> Choose the one (and make clear which one you have chosen) that makes most
> sense in your situation.
> Mike L.
> Rasch mailing list
> email: Rasch at acer.edu.au
> web: https://mailinglist.acer.edu.au/mailman/options/rasch/fabiol
Powered by Gmelius <https://gmelius.com/?ref=mail>
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Rasch