Among the varieties of logistic models, those attributed
to Birnbaum (involving the parameters of
item discrimination, item difficulty, and person
ability) and Rasch (involving only item difficulty
and person ability) have received attention. The
present research simulated the responses of 75
subjects responding to 30 items under the Birnbaum
model and then attempted a fit to the data
using the Rasch model. When item discriminations
varied from a variance of .05 to .25 within distributions
of different form (uniform, normal, and positively
skewed), the poorest overall fit appeared
within the uniform distribution. For each distribution
there was only a slight increase in the lack of
fit as the variances increased.
Dinero, Thomas E.; Haertel, Edward.
Applicability of the Rasch model with varying item discriminations.
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