Commentary on comparing translations of the EORTC QLQ-C30 using differential item functioning analyses.

The article comments on comparing translations of the European Organization for Research in the Treatment of Cancer questionnaire-C30 using differential item functioning (DIF) analysis. The author addresses the strengths and weaknesses of the paper. The first strength of the paper is the sheer magnitude of the data set that is analyzed; second, the reliance on an effect size statistic; and third, the consultation with bilingual experts regarding differences in nuance between different language versions of the test. On the other hand, the author also discusses the weaknesses of the paper.