Assessment of differential item functioning across English and Spanish versions of the Orofacial Esthetic Scale

Objectives: To investigate differential item functioning across the Spanish and English versions of the Orofacial Esthetic Scale (OES). Methods: OES data were collected from a consecutive sample of a total of 622 adult dental patients (311 English- and 311 Spanish-speaking adults) from HealthPartners dental clinics in Minnesota. We inspected boundary characteristic curves (BCCs) based on item response theory (IRT) in English speakers and Spanish speakers to examine differential item functioning (DIF). Using the Samejima's graded response model, we used the item response theory log-likelihood ratio (IRTLR) approach to test whether DIF was statistically significant. Results: Inspection of the BCCs did not reveal substantial differences in item difficulty and discrimination between English speakers and Spanish speakers. When IRTLR tests were performed for the seven OES items, no item was flagged with significant DIF after P-values were adjusted for multiple comparisons. Conclusions: Pooling of Orofacial Esthetic Scale (OES) data from English and Spanish-speaking dental patients for analysis and interpretation is supported by the absence of differential item functioning (DIF) across the two language groups.