Caronni Antonio, Scarano Stefano
Department of Neurorehabilitation Sciences, IRCCS Istituto Auxologico Italiano, Milan, Italy.
Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.
Disabil Rehabil. 2025 Apr;47(8):2134-2145. doi: 10.1080/09638288.2024.2391554. Epub 2024 Sep 2.
Differential Item Functioning (DIF), an item malfunctioning, causes Differential Test Functioning (DTF), thus biasing questionnaire measures. The current study evaluates the relationship between DIF and DTF for the Barthel Index and the Functional Independence Measure, likely the most used disability measures. The aim is to understand under which conditions DIF can be ignored as its DTF is negligible.
A simulation study was run. Disability measures were obtained for the Barthel Index and FIM motor domain using Rasch analysis with previously published item calibrations. Several DIF scenarios have been assessed. DTF was tolerable if ≤0.50 logits.
Simulations showed that the larger the DIF, the larger the DTF and that, keeping the overall DIF constant, the total number of items with DIF does not affect DTF. DIF of the items with the lowest or highest calibrations is the most dangerous. The DIF of central items should be so massive to matter in DTF terms that it is unlikely to happen in practice. The FIM robustness to DIF is better than that of the Barthel Index.
The FIM and the Barthel Index show remarkable robustness to DIF. Thanks to this feature, sample invariant, generalisable disability measures are available.
项目功能差异（DIF）作为一种项目故障，会导致测试功能差异（DTF），从而使问卷测量产生偏差。本研究评估了Barthel指数和功能独立性测量这两种可能是最常用的残疾测量方法中DIF与DTF之间的关系。目的是了解在哪些情况下，由于DTF可忽略不计，DIF可以被忽略。
进行了一项模拟研究。使用Rasch分析和先前发表的项目校准，获得了Barthel指数和FIM运动领域的残疾测量结果。评估了几种DIF情况。如果DTF≤0.50对数单位，则认为是可容忍的。
模拟结果表明，DIF越大，DTF越大，并且在总体DIF保持不变的情况下，存在DIF的项目总数不会影响DTF。校准值最低或最高的项目的DIF最危险。中心项目的DIF要大到在DTF方面产生影响，在实际中不太可能发生。FIM对DIF的稳健性优于Barthel指数。
FIM和Barthel指数对DIF表现出显著的稳健性。由于这一特性，可以获得样本不变、可推广的残疾测量方法。
