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These conditions are really pretty arbitrary. The an average of the four tests seems a reasonable aggregate to represent the semester’s performance, so this

main effect might be interesting, especially if the main effect pattern is descriptive for a majority of the exams. Four Exams

The marginal means are of dubious value, because it is unlikely that a group of students will practice for an exam with a variety of differently difficult practice problems. And so, it is not clear what population would be represented by the aggregate of the easier, harder, and similar difficulty performances

So, this main effect is only likely to be interesting if that main effect is descriptive, and so, it describes the behavior of those who practiced with similarly difficult, harder, and easier materials.

Remember – – non-significant lower-order effects that are involved in a significant higher order effect must be compared to the corresponding simple effects, to determine whether they are descriptive or misleading!!! 2-way Interaction Pairwise Comparisons You will usually want both sets of simple effects. One of those sets will be used to describe the pattern of the significant interaction. Each set will be used to determine if the corresponding main effect pattern is descriptive or misleading. Select the set of simple effects that most directly addresses the research question or research hypothesis The statement that, “The purpose of this study was to examine the Practice Difficulty on exam performance for each of the four exam given during the semester. .” makes the selection of the simple effects to use to describe the interaction straightforward. From this, we’ll want to focus on the simple effect of practice difficulty (easier, harder, similar) and then examine how this simple effect is different for each of the four exams.

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