A Power Formula for the SIBTEST Procedure for Differential Item Functioning
Zhushan Li · Applied Psychological Measurement · 2014
A power formula for the SIBTEST procedure for differential item functioning (DIF) is derived. The power of SIBTEST is related to the item response function (IRF) for the studied item, the latent trait distributions and the sample sizes for the reference and focal groups, and the proportion of each group in the sample. Based on the power formula, a method for calculating the sample size for a desired power level is presented. Monte Carlo simulation studies show that the theoretical values calculated from the formulas derived in the article are close to what are observed in the simulated data.