[Rasch] Re: Rasch Digest, Vol 35, Issue 12

Thomas Salzberger Thomas.Salzberger at wu-wien.ac.at
Wed Jul 2 06:59:45 EST 2008


Andrew Stephanou pointed out that we should be careful to distinguish 
between centralised and uncentralised thresholds.
By tau, I referred to the uncentralised thresholds (scaled 
'absolutely', i.e. with reference to the scale origin). The 
centralised thresholds are deviations from the item overall location. 
Centralised thresholds therefore add up to zero.


>1. For each item (or person), Rasch provides m-1 thresholds for the 
>m response categories.  The arithmetic mean of the m-1 thresholds 
>for each item(person) is then the item (or person) location or 
>commonly called item (or person) measure.  Am I right?

Yes, the mean of the thresholds (the tau parameters) is the (overall) 
item location (delta). However, for persons there is just one 
parameter, so no need to calculate a mean.

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