Evaluating the Impact of Multidimensionality on Unidimensional Item Response Theory Model Parameters

Authored by: Steven P. Reise , Karon F. Cook , Tyler M. Moore

Handbook of Item Response Theory Modeling

Print publication date:  December  2014
Online publication date:  November  2014

Print ISBN: 9781848729728
eBook ISBN: 9781315736013
Adobe ISBN: 9781317565703


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Commonly applied item response theory (IRT) measurement models stipulate a single continuous latent variable (typically labeled “θ”) to represent individual differences on a psychological construct. For example, Equation 2.1 is the item response curve for the commonly applied two-parameter logistic model (2PL) for dichotomous item responses, where αi is an item slope, βi is an item location, θ is a continuous latent variable, and 1.7 is a scaling factor that makes the value of the item slope parameter in logistic models comparable to a normal-ogive model. This scaling is important for researchers who wish to link IRT parameters with factor analytic results.

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