Assessing internal construct validity of DAPSA and DAPSA28 in psoriatic arthritis: a European observational study using confirmatory factor analysis and additional psychometric testing

Overall, the model fit was acceptable across model fit statistics, supporting internal construct validity, but some evidence of misfit at country level was disclosed. Our findings support acceptable internal consistency reliability, but DIF was found for sex and country. Based on mixed results of model fit and DIF, further investigation of these and other PsA disease activity measures is warranted.