Moderator effects (ie., interaction or synergy effects) are a topic of frequent interest in many sciences braches. A lot ink has been spilled over this topic (so did I, eg., here). However, in that post I did now show how to visualize error in case of nominal (categorical) independent variable, and categorical moderator. Luckily, visualization of this case is quite straight forward with ggplot2. First, some data and packages to be …