Item Response Theory Analysis and Differential Item Functioning of the Social Appearance Anxiety Scale.

This study examined the item- and scale-level functioning of the Social Appearance Anxiety Scale (SAAS) as well as differential functioning by gender using an item response theory (IRT) analysis. SAAS data collected from 840 college students were analyzed. A graded response model was used to analyze the 16 items comprising the SAAS. The measure was found to be unidimensional in its factor structure, and every item demonstrated high to very high ability to differentiate respondents varying in levels of the underlying trait (i.e., appearance concerns). In addition, we found evidence of differential item functioning (DIF) by gender for four items, corresponding to small effect sizes. Two of these items were related to internal experiences of appearance concerns (e.g., nervousness and discomfort when a flaw is noticed by others) that were more likely to be endorsed by women, and two of the items were related to external evaluative experiences related to appearance (e.g., missing opportunities and life being more difficult) that were more likely to be endorsed by men. Overall, the IRT and DIF results suggest that the SAAS effectively identifies appearance concerns among individuals with low to very high appearance concerns.