This procedure can calculate power, sample size and minimum difference for the 2-Sample t test.
1. Choose ProcessMA > Statistics > Power and Sample Size > 2-Sample t.
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 Alternate, select the type of test.
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.
You are the human resource manager and you want to assess if employee satisfaction has improved as compared to last year. From historical records you know that the standard deviation of the satisfaction index is 25. Determine the change in the satisfaction index you can detect for a sample size of 200, at a confidence level of 95% (a = 0.05) and power values of 0.7, 0.8, and 0.9?
1. Choose ProcessMA > Statistics > Power and Sample Size > 2-Sample t.
2. In Objective, select Find difference(s).
3. In Sample size(s), enter 200.
4. In Power value(s), enter 0.7, 0.8, 0.9.
5. In Standard deviation, enter 25.
6. In Alternate, select Greater than.
7. In Significance level, enter 0.05.
8. Click OK.
Interpretation
For a sample size of 200, you can detect a change in employee satisfaction index of 5.4324, 6.2268 and 7.3285 for powers of 0.7, 0.8 and 0.9 respectively.