Rule 1: Choose sensible contrasts. Remember that you want to compare only two chunks of variation and that if a group is singled out in one contrast, that group should be excluded from any subsequent contrasts. Rule 2: Groups coded with positive weights will be compared against groups coded with negative weights. So, assign one chunk of variation positive weights and the opposite chunk negative weights. Rule 3: If you add up the weights for a given contrast the result should be zero. Rule 4: If a group is not involved in a contrast, automatically assign it a weight of zero, which will
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