Centre for Research on Child and Adolescent Mental Health, Karlstad University, SE-651 88, Karlstad, Sweden.
BMC Med Res Methodol. 2019 Sep 5;19(1):185. doi: 10.1186/s12874-019-0828-3.
An overarching objective in research comparing different sample groups is to ensure that the reported differences in outcomes are not affected by differences between groups in the functioning of the measurement instruments, i.e. the items have to work in the same way for the different sample groups to be compared. Lack of invariance across sample groups are commonly called Differential Item Functioning (DIF). There is a sense in which the DIF of an item can be taken account of by resolving (splitting) the item into group specific items, rather than deleting the item. Resolving improves fit, retains the reliability and content provided by the item, and compensates for the DIF in estimation of person parameters on the scale of the instrument. However, it destroys invariance of the item's parameter value among the groups. Whether or not a DIF item should be resolved depends on whether the source of the DIF is relevant or irrelevant for the content of the variable. The present paper shows how external information can be used to investigate if the gender DIF found in the item "Stomach ache" in a psychosomatic symptoms scale used among adolescents may reflect abdominal pain because of a biological factor, the girls' menstrual periods.
Swedish data from the international Health Behaviour in School-aged Children study (HBSC) collected in 2005/06, 2009/10 and 2013/14 were used, comprising a total of 18,983 students in grades 5, 7 and 9. A composite measure of eight items of psychosomatic problems was analysed for DIF with respect to gender and menstrual periods using the Rasch model.
The results support the hypothesis that the source of the gender DIF for the item "Stomach ache" is a gender specific biological factor. In that case the DIF should be resolved if the psychosomatic measure is not intended to tap information about abdominal pain caused by a gender specific biological factor. In contrast, if the measure is intended to tap such information, the DIF should not be resolved.
The conceptualisation of the measure governs whether the item showing DIF should be resolved or not.
在比较不同样本组的研究中，一个总体目标是确保报告的结果差异不受测量工具功能差异的影响，即不同样本组比较时，项目必须以相同的方式运作。样本组之间缺乏不变性通常称为差异项目功能（DIF）。从某种意义上说，可以通过将项目分解为特定于组的项目（而不是删除项目）来考虑项目的 DIF。解决方法可以提高拟合度，保留项目的可靠性和内容，并在仪器量表上对个人参数的估计中补偿 DIF。但是，它会破坏项目参数值在组之间的不变性。是否要解决 DIF 项目取决于 DIF 的来源是否与变量的内容相关或不相关。本文展示了如何使用外部信息来调查青少年使用的身心症状量表中的项目“胃痛”中发现的性别 DIF 是否反映了由于生物因素（女孩的月经周期）引起的腹痛。
使用 2005/06 年、2009/10 年和 2013/14 年收集的国际青少年健康行为研究（HBSC）的瑞典数据，共包含 18983 名 5、7 和 9 年级的学生。使用 Rasch 模型，对与性别和月经周期有关的 8 项身心问题综合指标进行 DIF 分析。
结果支持这样的假设，即项目“胃痛”的性别 DIF 源是特定于性别的生物因素。在这种情况下，如果身心测量不打算获取由特定于性别的生物因素引起的腹痛信息，则应解决 DIF。相反，如果该测量旨在获取此类信息，则不应解决 DIF。
测量的概念化决定了显示 DIF 的项目是否应解决。
