This procedure can calculate power, sample size and minimum difference for the One-Way ANOVA.
1. Choose ProcessMA > Statistics > Power and Sample Size > One-Way ANOVA.
2. In Objective, choose what you want to calculate.
· If you want to find sample size(s):
- In Difference(s), enter one or more differences, separated by commas(,).
- In Power value(s), enter one or more power values, separated by commas(,).
· If you want to find difference(s):
- In Sample size(s), enter one or more sample sizes, separated by commas(,).
- In Power value(s), enter one or more power values, separated by commas(,).
· If you want to find power value(s):
- In Sample size(s), enter one or more sample sizes, separated by commas(,).
- In Difference (s), enter one or more differences, separated by commas(,).
3. In Standard deviation, enter the population standard deviation.
4. In Number of levels, enter the number of factor levels.
5. In Significance level, enter the desired significance level.
6. Click OK.
Sample size(s): Integer.
Difference(s): Numeric.
Power value(s): Numeric; Between 0 to 1; Must be greater than the significance level.
Standard deviation: Numeric.
Number of levels: Integer.
You want to study if 4 different types of treatment affect the growth of bacteria. Suppose you know that the average growth index for the all treatments is 34 and standard deviation is 3. If you need to detect a difference of 8 units in growth index and you have taken 6 samples per treatment, determine the power of your test for a confidence level of 99% (a = 0.01).
1. Choose ProcessMA > Statistics > Power and Sample Size > One-Way ANOVA.
2. In Objective, select Find power(s).
3. In Sample size(s), enter 6.
4. In Max Differences(s), enter 8.
5. In Standard deviation, enter 3.
6. In Number of levels, select 4.
7. In Significance level, enter 0.01.
8. Click OK.
Interpretation
For a sample size of 6 per treatment and 99% confidence level, the power for your test is 0.816 to detect a maximum difference of 8 units in growth index between treatment means.