Which type of graph is used to show treatment interactions?

The interaction plot is specifically designed to illustrate treatment interactions, making it the ideal choice for this question. When working with multiple factors in an experiment, an interaction plot allows researchers to visualize how different treatment levels affect the outcome variable in combination. It typically displays the means of the dependent variable for each combination of levels of the independent variables, highlighting how the effect of one variable depends on the level of another. This visual representation makes it easier to identify whether the interactions are significant, providing clear insights into the nature of the relationships among the variables.

In contrast, bar graphs are useful for comparing quantities across categories but do not effectively convey the interaction effects between multiple independent variables. Line graphs can represent trends over time or continuous data, but they may not adequately illustrate interactions between factors. Histograms are used to show the distribution of a single variable and are not suited for demonstrating relationships or interactions. Thus, interaction plots stand out for their capability to clearly depict complex relationships in a way that other types of graphs cannot.