How Many IRT Parameters Does It Take to Model Psychopathology Items?

Steven P. Reise, Niels G. Waller

Research output: Contribution to journalArticlepeer-review

88 Scopus citations


The authors compared the fit of the 2- and 3-parameter logistic models (2PLM; 3PLM) on 15 unidimensional factor scales derived from the Minnesota Multiphasic Personality Inventory - Adolescent item pool. Log-likelihood chi-square deviance tests indicated that a 3PLM provided an improved fit. However, residual statistics indicated that the difference in fit between the 2 models was negligible. An unexpected finding was that from 10% to 30% of the items had substantial lower asymptote parameters (c ≥ .10) when the scales were scored in the pathology or nonpathology directions. The authors argue that the large lower asymptote parameters are attributable to item-content ambiguity possibly caused by item-level multidimensionality. These findings suggest that the direction of scoring can critically affect an item response theory analysis.

Original languageEnglish (US)
Pages (from-to)164-184
Number of pages21
JournalPsychological Methods
Issue number2
StatePublished - Jun 2003


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