FAQ/WsubEffects - CBU statistics Wiki

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What is the difference between within subjects effects and within subjects contrasts in SPSS?

When SPSS performs a repeated measures analysis of variance, on a set of groups, say, it produces a couple of tables called within subjects effects and, just underneath, within subjects contrasts.

The within subjects effects table tests the general hypothesis that the group means are equal. To do this SPSS averages the differences between each group mean and the overall sample mean.

The within subjects contrasts table, by contrast (no pun intended!), tests a specific hypothesis. For example, does a particular pair of means differ from one other or, the default, are a particular means forming a linear trend.

There could be an overall difference amongst the group means (as seen in the within subjects effects table) even if a particular pair of group means do not differ from each other or form a particular ordering (as seen in the within subjects contrasts table).