Title page for ETD etd-07172008-130938

Type of Document Dissertation
Author Awuor, Risper Akelo
Author's Email Address rawuor@vt.edu
URN etd-07172008-130938
Title Effect of Unequal Sample Sizes on the Power of DIF Detection: An IRT-Based Monte Carlo Study with SIBTEST and Mantel-Haenszel Procedures
Degree PhD
Department Educational Leadership and Policy Studies
Advisory Committee
Advisor Name Title
Skaggs, Gary E. Committee Chair
Alexander, M. David Committee Member
Deater-Deckard, Kirby Committee Member
Miyazaki, Yasuo Committee Member
Wolfe, Edward W. Committee Member
  • Monte Carlo simulation
  • combination ratios
  • sample size
  • nominal p-value
  • DIF detection
  • DIF magnitude
  • statistical power
  • differential item functioning
Date of Defense 2008-06-19
Availability unrestricted
Risper Akelo Awuor - Abstract

This simulation study focused on determining the effect of unequal sample sizes on statistical power of SIBTEST and Mantel-Haenszel procedures for detection of DIF of moderate and large magnitudes. Item parameters were estimated by, and generated with the 2PLM using WinGen2 (Han, 2006). MULTISIM was used to simulate ability estimates and to generate response data that were analyzed by SIBTEST. The SIBTEST procedure with regression correction was used to calculate the DIF statistics, namely the DIF effect size and the statistical significance of the bias. The older SIBTEST was used to calculate the DIF statistics for the M-H procedure. SAS provided the environment in which the ability parameters were simulated; response data generated and DIF analyses conducted. Test items were observed to determine if a priori manipulated items demonstrated DIF. The study results indicated that with unequal samples in any ratio, M-H had better Type I error rate control than SIBTEST. The results also indicated that not only the ratios, but also the sample size and the magnitude of DIF influenced the behavior of SIBTEST and M-H with regard to their error rate behavior. With small samples and moderate DIF magnitude, Type II errors were committed by both M-H and SIBTEST when the reference to focal group sample size ratio was 1:.10 due to low observed statistical power and inflated Type I error rates.

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