An item response theory examination of the functionality appreciation scale

Area of Science:

• Psychology
• Body Image Research
• Psychometrics

Background:

• Functionality appreciation, valuing the body's capabilities, is key to positive body image.
• The Functionality Appreciation Scale (FAS) is a common tool, but its item properties require detailed analysis.
• Item response theory (IRT) offers advanced methods for evaluating measurement tools.

Purpose of the Study:

• To conduct an item-level analysis of the FAS using IRT.
• To evaluate item discrimination, difficulty, and measurement precision.
• To assess differential item functioning (DIF) across gender to ensure measurement invariance.

Main Methods:

• Applied a graded response model (GRM) to FAS data from 386 adults.
• Utilized confirmatory factor analysis (CFA) to confirm scale structure.
• Performed DIF analyses to examine gender-based item performance.

Main Results:

• CFA supported a unidimensional FAS structure.
• GRM indicated strong item discrimination (α = 2.79-4.08) and appropriate difficulty.
• No significant gender-based DIF was detected, supporting measurement invariance.

Conclusions:

• The FAS demonstrates strong reliability and utility in community samples.
• The scale offers optimal precision in the moderate range of functionality appreciation.
• Findings support the FAS's continued use in positive body image and well-being research.