[Rasch] Rasch & validity
S.Kreiner at biostat.ku.dk
Wed Jan 26 22:32:42 EST 2011
It depends on your definition of validity. I subscribe to Paul
Rosenbaum's (Psychometrika, 1989)definition of criterion related
construct validity requiring unidimensionality, monotonocity, local
independence and no DIF. For this reason, measurement by items from
Rasch models is valid because the Rasch models meet all these
requirements.(plus, of course, a number of other requirements that we
think are important - Rasch measurement is more than valid, it is also
objective and sufficient).
If you think about criterion validity and/or Cronbach & Meehl's
definition of construct validity you would not immediately think about
Rasch models, but it follows from Rosenbaum's results that if items
follow a Rasch model and if X is known to be positively related to the
latent trait, then X will also be positively related to the score. If X
is a criterion variable and X is not associated to the total score then
it follows that items cannot fit the Rasch model.
Den 26-01-2011 11:37, Anthony James skrev:
> Dear all,
> Validity is defined as "the degree to which a test measures what it is supposed to measure".
> How can fit to the Rasch model be evidence of validity?
> Can't we have a say, anxiety scale that perefctly fits the Rasch model but does not actually measure anxiety?
> How does Rasch analysis guarantee that a test actually test what it should test?
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Department of Biostatistics
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