Hendriks Jacqueline, Fyfe Sue, Styles Irene, Skinner S Rachel, Merriman Gareth
School of Public Health, Curtin University, Australia.
Australas Med J. 2012;5(5):251-61. doi: 10.4066/AMJ.2012.952. Epub 2012 May 31.
Measurement scales seeking to quantify latent traits like attitudes, are often developed using traditional psychometric approaches. Application of the Rasch unidimensional measurement model may complement or replace these techniques, as the model can be used to construct scales and check their psychometric properties. If data fit the model, then a scale with invariant measurement properties, including interval-level scores, will have been developed.
This paper highlights the unique properties of the Rasch model. Items developed to measure adolescent attitudes towards abortion are used to exemplify the process.
Ten attitude and intention items relating to abortion were answered by 406 adolescents aged 12 to 19 years, as part of the "Teen Relationships Study". The sampling framework captured a range of sexual and pregnancy experiences. Items were assessed for fit to the Rasch model including checks for Differential Item Functioning (DIF) by gender, sexual experience or pregnancy experience.
Rasch analysis of the original dataset initially demonstrated that some items did not fit the model. Rescoring of one item (B5) and removal of another (L31) resulted in fit, as shown by a non-significant item-trait interaction total chi-square and a mean log residual fit statistic for items of -0.05 (SD=1.43). No DIF existed for the revised scale. However, items did not distinguish as well amongst persons with the most intense attitudes as they did for other persons. A person separation index of 0.82 indicated good reliability.
Application of the Rasch model produced a valid and reliable scale measuring adolescent attitudes towards abortion, with stable measurement properties. The Rasch process provided an extensive range of diagnostic information concerning item and person fit, enabling changes to be made to scale items. This example shows the value of the Rasch model in developing scales for both social science and health disciplines.
旨在量化态度等潜在特质的测量量表通常采用传统心理测量方法来编制。拉施单维测量模型的应用可以补充或取代这些技术，因为该模型可用于构建量表并检验其心理测量特性。如果数据符合该模型，那么就会开发出一个具有不变测量特性（包括区间水平分数）的量表。
本文强调拉施模型的独特特性。以测量青少年对堕胎态度所编制的项目为例来说明这一过程。
作为“青少年关系研究”的一部分，406名12至19岁的青少年回答了与堕胎相关的10个态度和意向项目。抽样框架涵盖了一系列性经历和怀孕经历。对项目进行评估以确定其是否符合拉施模型，包括检查按性别、性经历或怀孕经历的项目功能差异（DIF）。
对原始数据集的拉施分析最初表明，一些项目不符合该模型。对一个项目（B5）重新计分并删除另一个项目（L31）后实现了拟合，如项目 - 特质交互总卡方不显著以及项目的平均对数残差拟合统计量为 -0.05（标准差 = 1.43）所示。修订后的量表不存在DIF。然而，项目在态度最强烈的人群中区分度不如在其他人群中。个人分离指数为0.82表明可靠性良好。
拉施模型的应用产生了一个有效且可靠的量表，用于测量青少年对堕胎的态度，具有稳定的测量特性。拉施过程提供了有关项目和个人拟合的广泛诊断信息，从而能够对量表项目进行调整。这个例子展示了拉施模型在为社会科学和健康学科编制量表方面的价值。
