Abstract: Moderation analysis is frequently applied to the studies of psychology and other social science disciplines. Empirical researchers working on experiments as well as questionnaire surveys are often interested in moderation effect because it can help explain how the direction and strength of the relationship between the independent and dependent variables will change. Given that the categorical variable is frequently encountered in social science researches, how to analyze moderation models with the categorical variable becomes a noteworthy issue. In the present study, we consider two scenarios: one is in a questionnaire survey, known as a cross-sectional or between-participant design; the other is in a longitudinal study at two time-points, or a two-condition experiment with the within-participant design. A procedure is proposed and recommended to analyze the moderation effect when the data is collected from the between-participant design and independent variable or moderator is a categorical variable. The first step is to examine whether the moderation effect is statistically significant by testing R2 change with and without the moderation term. If the moderation effect is not significantly different from zero, stop the moderation analysis. In the second step, the omnibus test is used to examine whether the k-1 simple slopes are zero, where k is the number of the categories. If the omnibus effect is not statistically significant, stop the moderation analysis. In the third step, the pairwise test is used to determine which of the k-1 simple slope is statistically significant. There are two pairwise test methods, namely the pick-a-point approach and Johnson-Neyman (J-N) approach. An example is given to illustrate how to conduct the proposed procedure by using SPSS macro PROCESS software. When the data is collected from the two-condition within-participant design, we may presume that every participant is assigned to both experimental treatments (X), and the dependent variable (Y) is observed under each condition. According to the general data input format (such as in SPSS), there is no X variable, and Y have two columns of values. So the above moderation analysis procedure is not suitable for this design. Then, another procedure is proposed and recommended for such kind of data to analyze the moderation effect, in which the only X is a categorical variable. The first step is to regress the difference in the repeated measured dependent variable Y2-Y1 on moderator Z. If the regression coefficient is not statistically significantly different from zero, stop the moderation analysis. In the second step, a simple slope test is conducted by the pick-a-point approach or Johnson-Neyman (J-N) approach. A second example is given to illustrate how to conduct the proposed procedure by using SPSS macro MEMORE software. Directions for future studies on categorical moderation are discussed at the end of the paper. The above methods and steps could be expended to more complicated moderation models, such as the moderated mediation model with a multi-categorical independent variable or moderator, the additive moderator model, and the multiplicative moderator model.

Key words: categorical variable, moderation effect, simple slope test, between-participant design, two-condition within-participant design

摘要： 类别变量在心理学和其他社科研究领域经常遇到，当自变量或调节变量为类别变量时，应当如何分析调节效应呢？详述了多类别变量的被试间设计和两水平被试内设计（因变量重复测量2次）的调节效应分析方法，并给出了分析流程。先进行调节效应的显著性检验，后用选点法或Johnson-Neyman法进行简单斜率检验。多类别变量被试间设计的简单斜率检验是先进行整体检验，后进行配对检验。用两个实际例子演示如何进行类别变量的调节效应分析，最后展望了两类设计的类别变量的调节研究的拓展方向，例如更复杂的类别变量的调节模型等。

关键词: 类别变量, 调节效应, 简单斜率检验, 被试间设计, 两水平被试内设计