Institution of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
Sleep Breath. 2013 Mar;17(1):157-65. doi: 10.1007/s11325-012-0664-8. Epub 2012 Feb 26.
Differential item functioning (DIF) is said to exist in an item if a subject's response to the item is affected by other aspects than that which the test is intended to assess. DIF might affect the validity of a test. The aim of this study was thus to examine whether any of the items in the Epworth Sleepiness Scale (ESS) exhibits DIF regarding age or gender, and if so, to which degree.
Using previously collected cross-sectional ESS data from 1,168 subjects with different clinical characteristics (61% males, mean age 67.8 year (SD 12.2 year)), ordinal regression as well as Rasch-based DIF analyses were performed.
Concerning age, both DIF analyses showed DIF for age in items 3 (inactive in a public place), 4 (passenger in a car), and 8 (in a car that has stopped in traffic). The Rasch model also showed DIF for gender in item 3. The DIF magnitudes as judged by McFadden pseudo-R (2) changes were, however, only minor.
ESS has small but reproducible DIF for age in items 3, 4, and 8. The detected DIF might be worth to consider in large-sample studies, although it probably has no effect on an individual basis.
如果一个项目的答案受到除测试所评估的内容以外的其他因素的影响，那么该项目就存在差异功能（DIF）。DIF 可能会影响测试的有效性。因此，本研究的目的是检验 Epworth 嗜睡量表（ESS）中的任何项目是否存在与年龄或性别有关的 DIF，如果存在，其程度如何。
使用先前收集的来自 1168 名具有不同临床特征的受试者（61%为男性，平均年龄为 67.8 岁（12.2 岁））的横断面 ESS 数据，进行了有序回归和基于 Rasch 的 DIF 分析。
关于年龄，两种 DIF 分析都显示出项目 3（在公共场所不活跃）、4（在汽车中作为乘客）和 8（在交通中停止的汽车中）的年龄 DIF。Rasch 模型还显示出项目 3 中的性别 DIF。然而，根据 McFadden 伪 R²变化来判断，DIF 的幅度很小。
ESS 在项目 3、4 和 8 中存在微小但可重复的年龄 DIF。尽管在个体基础上可能没有影响，但检测到的 DIF 可能值得在大样本研究中考虑。
