4.5. Blocking
In order to remove the additional variability in the data due to other external sources, blocking is often desired. Likewise, if the external variability is present due to two independent sources or is present in two orthogonal directions, two-way blocking using the Latin square design is often used. If the data are available for all the cells in the Latin square, the orthogonality of the two blocking variables and the treatment is automatically accomplished. Hence the Type I, II, III, and IV analyses are identical. A problem, however, occurs if the data are not available for certain cells or the blocks are of unequal size. The question in that case is, which analysis is appropriate? As the treatments are to be compared only after ...
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