Interaction (2 of 8)

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A look at the above graph shows that the effect of dosage differs as a function of task complexity. It also shows that the effect of task complexity differs as a function of drug dosage: The larger the drug dosage, the greater the difference between the simple task and the complex task. An interaction does not necessarily imply that the direction of an effect is different at different levels of a variable. There is interaction as long as the magnitude of an effect is greater at one level of a variable than at another. In the example, the complex task always takes longer than the simple task. There is an interaction because the magnitude of the difference between the simple and complex tasks is different at different levels of the variable drug dosage.