Lix Lisa M, Wu Xiuyun, Hopman Wilma, Mayo Nancy, Sajobi Tolulope T, Liu Juxin, Prior Jerilynn C, Papaioannou Alexandra, Josse Robert G, Towheed Tanveer E, Davison K Shawn, Sawatzky Richard
Department of Community Health Sciences, University of Manitoba, Winnipeg, MB, Canada.
School of Health and Human Performance, Dalhousie University, Halifax, NS, Canada.
PLoS One. 2016 Mar 21;11(3):e0151519. doi: 10.1371/journal.pone.0151519. eCollection 2016.
Self-reported health status measures, like the Short Form 36-item Health Survey (SF-36), can provide rich information about the overall health of a population and its components, such as physical, mental, and social health. However, differential item functioning (DIF), which arises when population sub-groups with the same underlying (i.e., latent) level of health have different measured item response probabilities, may compromise the comparability of these measures. The purpose of this study was to test for DIF on the SF-36 physical functioning (PF) and mental health (MH) sub-scale items in a Canadian population-based sample.
Study data were from the prospective Canadian Multicentre Osteoporosis Study (CaMos), which collected baseline data in 1996-1997. DIF was tested using a multiple indicators multiple causes (MIMIC) method. Confirmatory factor analysis defined the latent variable measurement model for the item responses and latent variable regression with demographic and health status covariates (i.e., sex, age group, body weight, self-perceived general health) produced estimates of the magnitude of DIF effects.
The CaMos cohort consisted of 9423 respondents; 69.4% were female and 51.7% were less than 65 years. Eight of 10 items on the PF sub-scale and four of five items on the MH sub-scale exhibited DIF. Large DIF effects were observed on PF sub-scale items about vigorous and moderate activities, lifting and carrying groceries, walking one block, and bathing or dressing. On the MH sub-scale items, all DIF effects were small or moderate in size.
SF-36 PF and MH sub-scale scores were not comparable across population sub-groups defined by demographic and health status variables due to the effects of DIF, although the magnitude of this bias was not large for most items. We recommend testing and adjusting for DIF to ensure comparability of the SF-36 in population-based investigations.
自我报告的健康状况测量工具，如简短健康调查问卷（SF-36），可以提供有关人群总体健康状况及其组成部分（如身体、心理和社会健康）的丰富信息。然而，当具有相同潜在（即潜伏）健康水平的人群亚组具有不同的测量项目反应概率时，就会出现项目功能差异（DIF），这可能会损害这些测量工具的可比性。本研究的目的是在一个基于加拿大人群的样本中，对SF-36身体功能（PF）和心理健康（MH）子量表项目进行DIF测试。
研究数据来自前瞻性的加拿大多中心骨质疏松症研究（CaMos），该研究在1996 - 1997年收集了基线数据。使用多指标多原因（MIMIC）方法进行DIF测试。验证性因素分析定义了项目反应的潜在变量测量模型，并且使用人口统计学和健康状况协变量（即性别、年龄组、体重、自我感知的总体健康状况）进行潜在变量回归，得出了DIF效应大小的估计值。
CaMos队列由9423名受访者组成；69.4%为女性，51.7%年龄小于65岁。PF子量表的10个项目中有8个以及MH子量表的5个项目中有4个表现出DIF。在PF子量表项目中，关于剧烈和适度活动、提拿和搬运杂货、步行一个街区以及洗澡或穿衣的项目观察到较大的DIF效应。在MH子量表项目中，所有DIF效应的大小都较小或中等。
由于DIF的影响，SF-36 PF和MH子量表得分在由人口统计学和健康状况变量定义的人群亚组之间不可比，尽管大多数项目的这种偏差幅度不大。我们建议对DIF进行测试和调整，以确保在基于人群的调查中SF-36的可比性。
