= Interaction plot
An interaction plot displays response means against levels of one factor, with separate lines for levels of another and optional panels for further factors. In an additive <linear regression>, the difference between two lines is constant across the horizontal factor, so the population-mean lines are parallel. Changing line separations or crossings show a <statistical interaction> on that response scale. Sample means may be nonparallel through noise, so the plot describes the effect pattern rather than replacing a formal <hypothesis test>.
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