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Step 1:
Select the table Compute Power or Sample Size for Two-Sample Chi-Squared Test from the Select Test Design & Goal window.
This is located under the Chi-Squared Test to Compare Two Proportions dropdown
This can be done using the radio buttons or alternatively, you can use the search bar at the end of the Select Test Design & Goal window.
Step 2:
Enter the parameter values for sample size calculation taken from the study design.
Step 3:
Enter the sample size. Once the sample size is entered, the power is calculated automatically. Make sure ‘Calculate the power’ is selected from the action dropdown menu.
| This gives rounded powers of 72%, 73% & 91% as per the study design Statement. |
Step 4:
An output statement is available for each scenario. Just click the corresponding column to get the output statement for that scenario.
The output statement appears at the bottom of nQuery. This can be printed or copy and pasted into any document.
| Output Statement: |
|
“A two group χ² test with a 5% two-sided significance level will have 73.33% power to detect the difference between a Group 1 proportion, π₁, of 0.6 and a Group 2 proportion, π₂ of 0.65 (odds ratio of 1.238) when the sample size in each group is 1250..” |
