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Marginal Maximum Likelihood Estimation for a Psychometric Model of Discontinuous Development IRT

Author(s):
Mislevy, Robert J.; Wilson, Mark
Publication Year:
1992
Report Number:
RR-92-74-ONR
Source:
ETS Research Report
Document Type:
Report
Page Count:
42
Subject/Key Words:
Office of Naval Research, Bayesian Statistics, Cognitive Development, Item Response Theory (IRT), Marginal Maximum Likelihood Estimation, Models, Psychometric Models, Test Theory

Abstract

(42pp.) Standard item response theory (IRT) models posit latent variables to account for regularities in students' performances on test items. They can accommodate learning only if the expected changes in performance are smooth and, in an appropriate metric, uniform over items. Wilson's "Saltus" model extends the ideas of IRT to development that occurs in stages, where expected changes can be discontinuous, show different patterns for different types of items, and even exhibit reversals in probabilities of success on certain tasks. Examples include Piagetian stages of psychological development and Siegler's rule-based learning. This paper derives marginal maximum likelihood (MML) estimation equations for the structural parameters of the Saltus model and suggests a computing approximation based on the EM algorithm. For individual examinees, Empirical Bayes probabilities of learning-stage are given, along with proficiency parameter estimates conditional on stage membership. The MML solution is illustrated with simulated data and an example from the domain of mixed number subtraction

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