Abstract

The two-wave mediation model is the most suitable model for examining mediation effects in a randomized intervention and includes measures taken at pretest and posttest. When using self-report measures, the meaning of responses may change for the treatment group over the course of the intervention and result in noninvariance across groups at posttest, a phenomenon referred to as response shift. We investigate how the mediated effect would be impacted by noninvariance when using sum scores (i.e., assuming invariance). In a Monte Carlo simulation study, the magnitude and proportion of items that had noninvariant intercepts, the direction of noninvariance, number of items, effect size of the mediated effect and sample size were varied. Results showed increased Type I and Type II errors due to a biased estimate of the intervention effect on the mediator resulting from noninvariance. Thus, measurement noninvariance could lead to erroneous conclusions about the process underlying the intervention.

摘要

双波调解模型是最适合检验随机干预中的调解效果的模型，包括在前测和后测中采取的措施。当使用自我报告措施时，在干预过程中，治疗组的反应含义可能会发生变化，并导致后测时各组间的非不变性，这种现象称为反应转变. 我们研究了在使用总分（即假设不变性）时非不变性如何影响中介效应。在 Monte Carlo 模拟研究中，具有非不变截距的项目的大小和比例、非不变性的方向、项目的数量、中介效应的效应大小和样本大小是不同的。结果显示，由于对非不变性对调解人的干预效果的估计有偏差，I 类和 II 类错误增加。因此，测量的非不变性可能导致对干预过程的错误结论。