![]() But extroverts perform better than introverts when they have ingested 4 mg of caffeine per kilogram of body weight. One example of a crossover interaction comes from a study by Kathy Gilliland on the effect of caffeine on the verbal test scores of introverts and extroverts (Gilliland,īetter than extroverts when they have not ingested any caffeine. Figure 8.4 shows the strongest form of this kind of interaction, called aĬrossover interaction. Variable again has an effect at both levels of the second independent variable, but the effects are in opposite directions. This is like the hypothetical driving example where there was a stronger effect of using a cell phone at night than during the day. (This is much like the study of Schnall and her colleagues where there was an effect of disgust for those high in private bodyĬonsciousness but not for those low in private body consciousness.) In the middle panel, one independent variable has a stronger effect at one level of the second independent variable than at Of the second independent variable but no effect at the others. In the top panel, one independent variable has an effect at one level The effect of one independent variable can depend on the level of the other in different ways. They were low in private body consciousness, then whether the room was clean or messy did not matter. If they were high in private body consciousness, then those in the messy room made harsher judgments. Schnall and her colleagues also demonstrated an interaction because the effect of whether the room was clean or messy on participants’ moral judgmentsĭepended on whether the participants were low or high in private body consciousness. ![]() This is an interaction because the effect of one independent variable (whether or not one receives psychotherapy) depends on the level It probably would not surprise you, for example, to hear that the effect of receiving psychotherapy is stronger among people who are highly motivated toĬhange than among people who are not motivated to change. Although this might seem complicated, you have an intuitive There is an i n teract i o n effect (or just “interaction”) when the effect of one independent variable depends on the level of another. But it also shows no overall advantage of one type of psychotherapy over the The longer the psychotherapy, the better it worked. The bottomĮxample, shows a clear main effect of psychotherapy length. ![]() Independent of each other in the sense that whether or not there is a main effect of one independent variable says nothing about whether or not there is a main effect of the other. It also shows a mainĮffect of time of day because driving performance was better during the day than during the night-both when participants were using cell phones and when they were not. The blue bars are, on average, higher than the red bars. The top panel of Figure 8.3 shows a main effect of cell phone use becauseĭriving performance was better, on average, when participants were not using cell phones than when they were. Thus there is one main effect to consider for each independent variable in the study. Levels of the other independent variable. A m a i n e f f e ct is the statistical relationship between one independent variable and a dependent variable-averaging across the In factorial designs, there are two kinds of results that are of interest: main effects and interaction effects (which are also called just “interactions”). Available under Creative Commons-NonCommercial-ShareAlike 4.0 International License.
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