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Item Response Theory of Philadelphia Naming Test (Fergadiotis et al., 2015)

posted on 01.06.2015, 00:00 authored by Gerasimos Fergadiotis, Stacey Kellough, William D. Hula
Purpose In this study, we investigated the fit of the Philadelphia Naming Test (PNT; Roach, Schwartz, Martin, Grewal, & Brecher, 1996) to an item-response-theory measurement model, estimated the precision of the resulting scores and item parameters, and provided a theoretical rationale for the interpretation of PNT overall scores by relating explanatory variables to item difficulty. This article describes the statistical model underlying the computer adaptive PNT presented in a companion article (Hula, Kellough, & Fergadiotis, 2015).
Method Using archival data, we evaluated the fit of the PNT to 1- and 2-parameter logistic models and examined the precision of the resulting parameter estimates. We regressed the item difficulty estimates on three predictor variables: word length, age of acquisition, and contextual diversity.
Results The 2-parameter logistic model demonstrated marginally better fit, but the fit of the 1-parameter logistic model was adequate. Precision was excellent for both person ability and item difficulty estimates. Word length, age of acquisition, and contextual diversity all independently contributed to variance in item difficulty.
Conclusions Item-response-theory methods can be productively used to analyze and quantify anomia severity in aphasia. Regression of item difficulty on lexical variables supported the validity of the PNT and interpretation of anomia severity scores in the context of current word-finding models.


This research was supported by VA Rehabilitation Research and Development Career Development Award C7476W (awarded to William Hula) and the VA Pittsburgh Healthcare System Geriatric Research Education and Clinical Center. The authors would like to acknowledge the helpful assistance of Daniel Mirman and Myrna Schwartz. The contents of this article do not represent the views of the Department of Veterans Affairs or the United States government.