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Critique of enhanced power claimed for Quasi-ANCOVA and Dual-Centered ANCOVA

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  • B Wade Brorsen
  • Hua Lin
  • Robert E Larzelere

Abstract

Two related methods, Quasi-ANCOVA and Dual-Centered ANCOVA, have recently been suggested as a way to get greater power when analyzing data from a before and after study. Both methods use group-mean centering where the groups are the treatment and comparison groups. Group-mean centering creates a generated regressor problem. When the estimated standard errors are corrected for the generated regressor problem, there is no longer any gain in power. The corrected Quasi-ANCOVA estimates are identical to those from ANOVA and the corrected Dual-Centered ANCOVA estimates are identical to those from the differences model. These conclusions are derived analytically and also verified using a Monte Carlo simulation.

Suggested Citation

  • B Wade Brorsen & Hua Lin & Robert E Larzelere, 2025. "Critique of enhanced power claimed for Quasi-ANCOVA and Dual-Centered ANCOVA," PLOS ONE, Public Library of Science, vol. 20(1), pages 1-6, January.
    • Handle: RePEc:plo:pone00:0317860
    DOI: 10.1371/journal.pone.0317860
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