Analysis of Covariance

Objective

To adjust data for the effects of other variables and thus permit analysis of variance to be used effectively.

Examples/Applications

• Sample matching
• Post-experimental adjustments

Assumptions

• Same as analysis of variance
• Regressions for treatment groups have parallel slopes

Mechanics

• Uses regression to statistically match groups by canceling out the effects of initial score differences
• Applies analysis of variance to adjusted scores

Seminal Articles/Texts

• Barrow, Lionel; Journal of Advertising Research, May 1964
• Green, Paul and Tull, Donald; Journal of Advertising Research, June 1964

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