The lines may not always cross as dramatically, and the appearance of the graph also depends on what variable the x-axis explores, but charting the means is often the only way to get a sense of what’s going on as far as main effects and interactions. The actual statistical test that is conducted to see if an interaction is significant is basically to look at the lines on the graph and judge if they are parallel. If there is no interaction, the effect of one independent variable on the dependent variable is the same for each level of the other independent variable. So each line raises or lowers
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