G. Lee et al., Comparison of dichotomous and polytomous item response models in equating scores from tests composed of testlets, APPL PSYC M, 25(4), 2001, pp. 357-372
The performance of two polytomous item response theory models was compared
to that of the dichotomous three-parameter logistic model in the context of
equating tests composed of testlets. For the polytomous models, testlet sc
ores were used to eliminate the effect of the dependence among within-testl
et items. Traditional equating methods were used as criteria for both. The
equating methods based on polytomous models were found to produce results t
hat more closely agreed with the results of traditional methods.