Minitab offers different confidence interval methods for comparing treatment means. Dunnet's method is available for comparisons with a control. The formula for the confidence intervals is:
The formula for the test statistic is:
The adjusted p-value is the result of integrating the distribution that Dunnett proposes for the test statistic. For details, see the references below.
|the least squares mean for the ith factor level or factor level combination |
|the least squares mean for the jth factor level or factor level combination |
|D1-α, k-1, u||the upper α percentile of the distribution that Dunnett proposes with k − 1 comparisons and u degrees of freedom|
|α||the simultaneous probability of making a Type I error|
|k||the number of means to compare|
|u||the degrees of freedom for error from the model|
|SEE||the standard error of the estimated difference between the least squares means|
1 Dunnett, C. W. (January 01, 1955). A multiple comparison procedure for comparing several treatments with a control. Journal of the American Statistical Association, 50, 1096-1121.
2 J.C. Hsu (1996). Multiple Comparisons: Theory and methods. Chapman & Hall.