Measurement invariance and differential item functioning of the Functionality Appreciation Scale (FAS) in Colombia and Spain

The Functionality Appreciation Scale (FAS) is increasingly used in diverse national and linguistic contexts. However, limited work has assessed the extent to which the instrument demonstrates measurement invariance and differential item functioning (DIF) across nations and respondent characteristics. Here, we examined measurement invariance and DIF of the FAS using archival data from adults in Colombia (Mebarak et al., 2023) and Spain (Zamora et al., 2024). Participants included 1,420 (women n = 804, men n = 616) respondents from Colombia and 838 (women n = 415, men n = 423) respondents from Spain who completed translations of the FAS. Confirmatory factor analysis supported a unidimensional structure of the FAS in both national groups. Additionally, the FAS achieved full measurement invariance (up to latent mean invariance) across both groups. We also found that the FAS lacked DIF as a function of age, body mass index (BMI), and gender identity across both national groups. Older participants (relative to younger participants), men (relative to women), and participants with lower BMIs (relative to those with higher BMIs) had higher FAS scores. These results support the notion that the FAS is measuring a common underlying construct across these national groups and respondent characteristics.