Differential item functioning between English, German, and Spanish PROMIS® physical function ceiling items

Area of Science:

• Health Measurement
• Psychometrics
• Cross-cultural Adaptation

Background:

• Patient-reported outcome measures (PROMs) require rigorous validation for international use.
• The Patient Reported Outcomes Measurement Information System (PROMIS®) Physical Function item bank is a widely used tool for assessing physical functioning.
• New items require cross-cultural validation to ensure measurement equivalence.

Purpose of the Study:

• To evaluate the psychometric properties and cross-cultural validity of German and Spanish translations of 35 new items in the PROMIS® Physical Function item bank 2.0.
• To assess differential item functioning (DIF) for these translated items across general population samples from Argentina, Germany, and the United States.

Main Methods:

• Data were collected from 3601 participants (1001 Spanish, 1000 German, 1600 English) via online panels.
• Differential item functioning (DIF) was assessed using a multiverse analysis approach within a logistic ordinal regression framework.
• Analytic choices were systematically varied to ensure robustness of DIF identification.

Main Results:

• Translated items generally demonstrated unidimensionality, monotonicity, and local independence.
• A multiverse analysis identified consistent DIF in four items across languages.
• The impact of DIF on test scores was negligible at the test level, with minimal differences observed between Argentina and the US/Germany after DIF correction.

Conclusions:

• The PROMIS® Physical Function items demonstrate universal applicability across general populations in Argentina, Germany, and the U.S.
• Sensitivity analyses confirmed the robustness of DIF identification across various analytical decisions.
• Multiverse analysis offers a valuable approach for addressing challenges in DIF identification.