Comparing Means with a Control (2 of 4)
The procedure for comparing each experimental mean with the control mean is called "Dunnett's test" after the statistician who developed it. Dunnett's test controls the EER and is more powerful than tests designed to compare each mean with each other mean. Dunnett's test is conducted by computing a t-test between each experimental group and the control group using the formula:
where Mi is the mean of the ith experimental group, Mc is the mean of the control group, MSE is the mean square error as computed from the analysis of variance, and nh is the harmonic mean of the sample sizes of the experimental group and the control group. The degrees of freedom (df) for the test are equal to N-a where N is the total number of subjects in all groups and "a" is the number of groups (including the control).