Which non-orthogonal planned contrast compares the mean of each condition (except the first) to the mean of all previous conditions combined?

• A. Deviation contrast
• B. Difference contrast
• C. Direct oblimin
• D. Discriminant analysis

Answer: (B)

In planned contrasts for ANOVA, you can test very specific patterns across the condition means. This item describes a pattern where, for every condition beyond the first, you compare its mean to the mean of all the previous conditions combined. In other words, each successive condition is evaluated against the average of everything that came before it.

That exact pattern is what is captured by the difference contrast. It creates non-orthogonal comparisons because each new contrast shares information with the earlier ones—the mean of previous conditions is used repeatedly as a reference. The result is a set of tests that are not mutually independent, which is characteristic of non-orthogonal contrasts.

The other options don’t fit this description. Deviation contrasts compare each level to the grand mean of all levels, not to the mean of preceding levels. Direct oblimin is a rotation method used in factor analysis, not a contrast type. Discriminant analysis is a different multivariate technique entirely.

So, the described plan aligns with the difference contrast.