Computing Tests of Comparisons (1 of 6)

Planned Comparisons
A method for computing planned comparisons among means is described in another section. That method is generalized here so that it can be used with unequal as well as with equal sample sizes.

First compute

where L = ΣMiai and

ai is the coefficient applied to the ith mean
ni is the sample size of the ith group
Mi is the ith mean
MSE is from the analysis of variance. It equals SSE/dfe
The t is based on dfe = N-a degrees of freedom where N is the total number of subjects and "a" is the number of groups.