Differential Item Functioning between English, German, and Spanish PROMIS® Physical Function Ceiling Items

Purpose— We investigated the validity of the German and Spanish translations of 35new high functioning items added to the Patient Reported Outcomes Measurement InformationSystem (PROMIS®) Physical Function item bank 2.0. We assessed differential item functioning(DIF) between three general population samples from Argentina, Germany, and the UnitedStates.Methods—PROMIS Physical Function data was collected in online panels from 3601individuals (mean age, 41.6 years old; range, 35.6-44.9; 53.7% female). Of these, 1001participants completed the Spanish version, 1000 completed the German version, and 1600completed the English version. DIF was assessed by a multiverse analysis that systematicallyvaried analytic choices across the entire range of plausible options within the logistic ordinalregression framework.Results—Translated items generally met the assumptions of unidimensionality,monotonicity, and local independence. The 272 different analyses suggest consistent DIFbetween languages in four items. Test characteristic curves suggested that the magnitude andimpact of DIF on the test scores were negligible for all items at the test level. After correcting forpotential DIF, we observed greater scoring for physical functioning in Argentina compared to theUS, Cohen’s d = 0.25, [0.17, 0.33], and Argentina compared to Germany, Cohen’s d = 0.23,[0.15, 0.32].Conclusions—Our findings support the universal applicability of PROMIS PhysicalFunction items across general populations in Argentina, Germany, and the U.S. The sensitivityanalyses indicate that the identification of DIF items was robust for different data analyticdecisions. Multiverse analysis is a promising approach to address lack of clear cutoffs in DIFidentification.