How many IRT parameters does it take to model psychopathology items?
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 > or = .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.
Reise
Steven P
SP
Department of Psychology, University of California, Los Angeles 90095, USA. reise@psych.ucla.edu
Waller
Niels G
NG
D000293:Adolescent; D016009:Chi-Square Distribution; D003627:Data Interpretation, Statistical; D005260:Female; D006801:Humans; D016015:Logistic Models; D008950:MMPI; D008297:Male; D015233:Models, Statistical; D010552:Personality Assessment; D011594:Psychometrics; D011599:Psychopathology / Q000706:statistics & numerical data*; D012649:Self Concept