What best describes planned contrasts?

• A. A method for measuring the strength of relationship between two variables.
• B. A test used to estimate population parameters.
• C. A set of comparisons between group means that are planned before data collection and partition the variance with greater power than post hoc tests.
• D. A type of regression designed for non-linear relationships.

Answer: (C)

Planned contrasts test specific hypotheses about how group means differ, with the plan decided before data collection. Because you specify in advance which group differences matter and limit the number of comparisons, these tests focus on those particular questions and generally have more power to detect the expected differences than running many post hoc tests after the fact. In practice, planned contrasts test linear combinations of the group means and use the same error term from the overall ANOVA to determine significance, allowing precise evaluation of targeted hypotheses—such as comparing each treatment to a control or assessing a monotonic trend across ordered groups.

This approach contrasts with methods used to measure relationships between variables (that would be about correlation), estimation of population parameters (which involves estimating means or other values with confidence intervals), or modeling non-linear relationships (nonlinear regression).