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<font face="Times New Roman">Anthony,<br>
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 </font>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).<br>
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
Den 26-01-2011 11:37, Anthony James skrev:
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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