Covariance Analysis for Split-Plot and Split-Block Designs

Commentaries are informative essays dealing with viewpoints of statistical practice, statistical education, and other topics considered to be of general interest to the broad readership of The American Statistician.Commentaries are similar in spirit to Letters to the Editor, but they involve longer discussions of background, issues, and perspectives.All commentaries will be refereed for their merit and compatibility with these criteria.Proper methodology for the analysis of covariance for experiments designed in a split-plot or split-block design is not found in the statistical literature.Analyses for these designs are often performed incompletely or even incorrectly.This is especially true when popular statistical computer software packages are used for the analysis of these designs.This article provides several appropriate models, ANOVA tables, and standard errors for comparisons from experiments arranged in a standard split-plot, split.split-plot, or split-block design where a covariate has been measured on the smallest size experimental unit.