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occur, for example, in survey research. When cell ns are unequal, a researcher has a choice between computing unweighted means or weighted means. Unweighted means are simple averages of cell means. These are the means that were used in the previous analyses. Weighted means are weighted averages of cell means in which the weights are the sample cell sizes, njk. Consider again the weight-loss data in which observation Y322 is missing. Unweighted and weighted sample means for treatment level a2 where observation Y322 is missing are, respectively,

nj. is the number of observations in the jth level of treatment A. The null hypothesis using weighted cell means for treatment A is n11^n + n12^12 n21^21 + n22^22 n Hq.---= u ni. n2.

The coefficient matrix for computing SSA is

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