Replicates are multiple experimental runs with the same factor settings.
Use the number of replicates to estimate how many experimental runs to include in the design. If you enter a power and maximum difference, Minitab calculates the number of replicates. Because the numbers of replicates are given in integer values, the actual power may be greater than your target value. If you increase the number of replicates, the power of your design also increases. You want enough replicates to achieve adequate power.
Because the replicates are integer values, the power values that you specify are target power values. The actual power values are for the number of replicates and the number of center points in the designed experiment. The actual power values are at least as large as the target power values.
In these results, Minitab calculates the number of replicates to reach a target power of 80% and a target power of 90%. To detect a difference of 2.0, the design requires 3 replicates to achieve either the target of 80% or the target of 90%. The power for the design with 2 replicates is less than the target power of 80%. To detect the smaller difference of 1.8, 3 replicates gives more than 80% power but not more than 90% power. To detect the smaller difference with 90% power, the designed experiment needs 4 replicates. Because the numbers of replicates are integers, the actual powers are greater than the target powers.
These results also show that the factor with the most levels has 4 levels. These results are accurate for the 4-level factor. The number of replicates could be different for the two 3-level factors, especially if the actual power is much greater than the target power.
Power and Sample Size
General Full Factorial Design
α = 0.05 Assumed standard deviation = 1.8
Factors: 3 Number of levels: 4, 3, 3
Include terms in the model up through order: 2
Not including blocks in model.
Maximum Total Target
Difference Reps Runs Power Actual Power
2.0 3 108 0.8 0.932615
2.0 3 108 0.9 0.932615
1.8 3 108 0.8 0.867493
1.8 4 144 0.9 0.952918