Which contrast is a non-orthogonal planned contrast that compares the mean of each condition (except the last) to the overall mean of all subsequent conditions combined?

Which contrast is a non-orthogonal planned contrast that compares the mean of each condition (except the last) to the overall mean of all subsequent conditions combined?

• A. Difference contrast
• B. Polynomial contrast
• C. Helmert contrast
• D. Simple contrast

Answer: (C)

Helmert contrasts test ordered differences by contrasting each condition with the average of the later conditions. With five conditions, you’d have four contrasts: first, compare the mean of condition 1 to the mean of conditions 2–5; second, compare condition 2 to the mean of conditions 3–5; third, compare condition 3 to the mean of conditions 4–5; and fourth, compare condition 4 to condition 5. This pattern directly matches the idea of looking at whether earlier conditions differ from the later ones on average, making it the best choice for the described contrast. These contrasts are planned to test a specific progression across the conditions, unlike other contrasts that focus on comparisons to a baseline, adjacent levels, or overall trends.

Helmert contrasts test ordered differences by contrasting each condition with the average of the later conditions. With five conditions, you’d have four contrasts: first, compare the mean of condition 1 to the mean of conditions 2–5; second, compare condition 2 to the mean of conditions 3–5; third, compare condition 3 to the mean of conditions 4–5; and fourth, compare condition 4 to condition 5. This pattern directly matches the idea of looking at whether earlier conditions differ from the later ones on average, making it the best choice for the described contrast. These contrasts are planned to test a specific progression across the conditions, unlike other contrasts that focus on comparisons to a baseline, adjacent levels, or overall trends.