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A before/ after difference can simply be due to a decreasing trend. A simple before/ after comparison using only Queensland data is not sufficient to test if the tax increase changed alcohol consumption because there is no comparision group.We have collected data on alcohol consumption in 20, and want to test if the change in alcohol consumption (measured in number of standard drinks consumed per month) in Queensland was different from other states. Suppose that in Australia, Queensland implemented an increase in alcohol tax in 2018 and there was no change in tax in any other states (e.g. Categorical independent variable and categorical moderator Numeric independent variable and numeric moderatorįor instances with a categorical independent variable and numeric moderator, the analytic strategy would be the same as conducting a moderation analysis with a numeric independent variable with categorical moderator.Numeric independent variable and categorical moderator.Categorical independent variable and categorical moderator.In this tutorial, we will examine three scenarios. Do states (moderator) change the effect of time (independent variable) on alcohol consumption (dependent variable)? Here, we want to test if the change over time (effect of time before and after a new tax rule) was the same across states. Does the implementation of an alcohol tax in one state change alcohol consumption, compared to other states without changes in tax?.In this example, we want to see if the effect of psychotherapy on depression is the same across sex (i.e.Is the effect of psychotherapy (independent variable) on depression (dependent variable) stronger for females than for males (moderator: sex)?.In other words, it is used to examine whether the moderator will change the strength of the relationship between the independent and dependent variables. Moderation analysis is used to examine if the effect of an independent variable on the dependent variable is the same across different levels of another independent variable (moderator). The tutorial is based on R and StatsNotebook, a graphical interface for R.Īssumed knowledge in this tutorial: Linear regression