[Rasch] Rasch & validity

Svend Kreiner 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?
> Cheers
> Anthony
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Svend Kreiner
Department of Biostatistics
University of Copenhagen

Øster farimagsgade 5, entr. B
P.O. Box 2099
DK-1014 Copenhagen K, Denmark

Email: S.Kreiner at biostat.ku.dk
Phone: (+45) 35 32 75 97

Fax: (+45) 35 32 79 07

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