Contrast Analysis

Planned contrast analysis is a parametric hypothesis-testing method that evaluates specific, theoretically motivated comparisons among group means — comparisons that the researcher specifies before data collection, not in response to observed patterns. Formalized comprehensively by Rosenthal, Rosnow, and Rubin (2000), the approach assigns a set of contrast coefficients to the groups being compared, with the constraint that the coefficients sum to zero, and then tests whether the resulting weighted combination of means differs significantly from zero.