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Tukey

The Tukey strategy is used to test all the two and two combinations between the levels of a factor.

Example: Consider the data set of the following table.

Factor Fiber Strenght
15 7
15 7
15 15
15 11
15 9
20 12
20 17
20 12
20 18
20 18
25 14
25 18
25 18
25 19
25 19
30 19
30 25
30 22
30 19
30 23
35 7
35 10
35 11
35 15
35 11

click here to download the data

 

To use the tool Tukey, the user must follow these steps: 

1. Access the menu:

Action $ \blacktriangleright $ ANOVA $ \blacktriangleright $ Multiple Comparisons $ \blacktriangleright $ Tukey

2. The following screen will be shown;

 

3. With the cursor in the field Factor select the column that refer to the factor (without the name of the column). With the cursor in the field Response Variable select the column that refers to the Response Variable (without the name of the column)

4. Choose the Significance Level α. In this case, we will use α=0.05.

5. In Show Results choose one of the options. We suggest the option New Sheet because Action does not have the undo command.

6. To finish, click Ok.

Results and Interpretation

Once the process is finished, the following results will be shown.



  • The Tukey test assess the equality between the values, so it is a hypothesis test. In these results we see that the equality hypothesis is rejected between the levels 20-15, 25-15, 30-15, 30-20, 35-25 and 35-30, because they have p-value < 0.05.
  • Another way to assess if there is equality between the levels or not is using the confidence levels and the chart. If the value is zero, it belongs to the confidence interval and we do not reject the hypothesis of equality between the levels.