Evaluation of psychometric properties of the Dental Anxiety Inventory (DAI‐36) questionnaire using iterative hybrid ordinal logistic: Differential item functioning (DIF)

OBJECTIVES: Dental Anxiety Inventory (DAI‐36) questionnaire is an instrument for assessing dental anxiety. The different perceptions of the questionnaire items in the individual at the same level of underlying dental anxiety may lead to different reported dental anxieties. This study aims to determine the differential item functioning (DIF) of the DAI‐36 measure items. METHODS: The DAI‐36 was completed by 950 participants. An iterative hybrid ordinal logistic regression model was used to detect DIF across gender, education, and age groups. DIF analysis was done by lordif package in R3.1.3 software. RESULTS: The chi‐square statistics declared 7, 7, and 4 nonuniform DIF items, and 2, 5, and 4 uniform DIF items across gender, education, and age groups, respectively. ΔR2 was always lower than 0.07 in all uniform and nonuniform DIF items. However, Δβ1 revealed significant uniform DIF in items 1 and 8 across gender (Δβ1(item 1) = 0.0137, Δβ1(item 8) = 0.0124) and items 22 and 27 across age categories (Δβ1(item 22) = 0.0110, Δβ1(item 27) = 0.0136). CONCLUSIONS: DIF items had no large magnitude or cancel out each other, so statements phrased in the DAI‐36 questionnaire have equivalent meaning across participants, regardless of their gender, education, and age groups.