This study investigated the adequacy of the Rasch
model in providing objective measurement when
equating existing standardized reading achievement
tests with groups of examinees not widely separated
in ability. To provide the context for the assessment
of objectivity with the Rasch model, information
relevant to several assumptions of the model was
provided. An anchor test procedure was used to
equate the various pairs of existing achievement
tests. Despite the considerable lack of fit of the
data to the model found for all tests used, the
Rasch difficulty estimates were reasonably invariant
for replications with random samples as well as
samples that differed in ability by one grade level.
Furthermore, with the exception of the data for one
test pair and one grade level, the Rasch model
using the anchor test procedure provided a reasonably
satisfactory means of equating three test pairs
on the log ability scale for the examinees at two
Slinde, Jeffrey A & Linn, Robert L. (1979). The Rasch model, objective measurement, equating, and robustness. Applied Psychological Measurement, 3, 437-452. doi:10.1177/014662167900300402
Slinde, Jeffrey A.; Linn, Robert L..
The Rasch model, objective measurement, equating, and robustness.
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