Differential Item Functioning of the Jaw Functional Limitation Scale

Area of Science:

• Dental research
• Psychometrics
• Health outcomes measurement

Background:

• The Jaw Functional Limitation Scale (JFLS) is used to assess limitations in jaw function.
• Ensuring the JFLS is unbiased across different demographic groups is crucial for accurate patient assessment.

Purpose of the Study:

• To evaluate differential item functioning (DIF) in the JFLS based on gender, age, and language (English vs. Spanish).
• To determine if the JFLS summary score provides psychometrically robust comparisons across diverse patient groups.

Main Methods:

• Item response theory (IRT) analysis using Samejima's graded response model was applied to JFLS data from 1,678 adult dental patients.
• The IRT log-likelihood ratio approach was used to detect DIF, with magnitude assessed by noncompensatory DIF (NCDIF) and Cohen's effect sizes.

Main Results:

• Essential unidimensionality of the JFLS was confirmed, though some local dependence was noted.
• A few items showed statistically significant DIF, but all had NCDIF indices below the 0.096 cutoff and small effect sizes (≤ 0.2).
• Test characteristic curves indicated minimal differences in expected scores.

Conclusions:

• The JFLS summary score is psychometrically robust for comparisons across English/Spanish speakers, males/females, and younger/older dental patients.
• The overall magnitude and practical impact of DIF on the JFLS were found to be minimal.