What is a simple contrast in planned comparisons?

• A. A non-orthogonal planned contrast that compares each condition to the mean of the first or last condition.
• B. An orthogonal post hoc comparison among all pairwise means.
• C. A comparison of the grand mean to each individual condition mean.
• D. A contrast that compares consecutive conditions only.

Answer: (A)

A simple contrast in planned comparisons tests how each condition differs from a single reference level, usually the first (or sometimes the last) condition. You set up contrasts that compare every other condition’s mean to the mean of that reference condition, so you can see, for example, how condition two differs from condition one, how condition three differs from condition one, and so on. Because all comparisons share the same baseline, the contrast vectors are not independent of each other, making them non-orthogonal.

This matches the idea described: a planned, non-orthogonal simple contrast that compares each condition to the mean of the first or last condition. The other options describe different kinds of comparisons—orthogonal post hoc pairwise tests, contrasts against the grand mean, or focusing only on consecutive conditions—not the baseline-versus-everything simple contrast.