Enter your data for Comparisons

To perform this analysis in Minitab, go to the menu that you used to fit the model, then choose Comparisons.

Complete the following steps to specify the response and select the multiple comparison method.

  1. From Response, select the response variable.
    Note

    Only response variables with up-to-date models from the same analysis are in the list. If you cannot see a response that you want, refit the model. For more information, go to Stored model overview.

  2. From Type of comparison, select one of the following options:
    • Pairwise: Compare all of the means to each other for the terms that you select.
    • With a control: Compare treatment means to the mean of a control group. When this method is suitable, it is inefficient to use pairwise comparisons because the confidence intervals are wider and the hypothesis tests are less powerful for a specified simultaneous confidence interval.
  3. Under Method, select one or more comparison methods that you want to use.
    • Tukey: Compares all pairs of groups, while controlling the simultaneous confidence level. The Tukey method is not available if you choose to make comparisons with a control. For example, a plastics company chooses Tukey's method to compare the strengths of five types of plastic, while maintaining a 95% simultaneous confidence level.
    • Fisher: Compares all pairs of groups, while controlling the individual confidence level. Fisher's method is less common than Tukey's method because it does not control the simultaneous confidence level, which often decreases to unacceptable levels. For example, a plastics company chooses Fisher's method to compare the strengths of five types of plastic, while maintaining a 95% individual confidence level. After the analysis, the output indicates that the simultaneous confidence level is 71.73%, which is too low.
    • Dunnett: Compare treatment means to the mean of a control group, while controlling the simultaneous confidence level. The Dunnett method is not available if you select Pairwise comparisons. For comparisons with a control, Dunnett's method is usually more powerful than the Bonferroni and the Sidak methods. For example, a plastics company chooses Dunnett's method to compare the strengths of four new plastic formulations to the formulation that the manufacturer currently uses.
    • Bonferroni: Compare groups while controlling the simultaneous confidence level.
    • Sidak: Compare groups while controlling the simultaneous confidence level.
  4. In Choose terms for comparisons, select the terms that you want to compare.
  5. If you chose With a control from Type of comparison, under Control levels, select a control level for each factor that you specified for comparison.
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