Date of Graduation


Document Type


Degree Name

Doctor of Philosophy in Educational Statistics and Research Methods (PhD)

Degree Level



Rehabilitation, Human Resources and Communication Disorders


Ronna Turner

Committee Member

Wen-Juo Lo

Second Committee Member

Andronikos Mauromoustakos


Differential Item Functioning, Item Response Theory, Local Spatial Modeling, Measurement and Evaluation, Questionnaire Design, Rasch Modeling


Mappings of spatially-varying Item Response Theory (IRT) parameters are proposed, allowing for visual investigation of potential Differential Item Functioning (DIF) based upon geographical location without need for pre-specified groupings and before any confirmatory DIF testing. This proposed model is a localized approach to IRT modeling and DIF detection that provides a flexible framework, with current emphasis being on 1PL/Rasch and 2PL models. Applications to both simulated and empirical survey data, utilizing a box-car kernel weighting scheme with several fixed bandwidths on irregular spatial lattices, are presented both to demonstrate the methodology and to illustrate the benefit of localized IRT modeling. There is not only practical value with this method but also visual appeal when initial attempts to consider measurement invariance are being made across national, state, or other political and geographical boundaries, especially when comparisons are made to traditional DIF techniques. This approach, making use of surface mappings of estimated item parameters, serves to detect DIF across space without a priori groupings, thereby identifying regional disparities and latent spatial trends in item functionality that may be unobservable on a more aggregate, global level.