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Step 1:
Select the Two Sample Student’s T-test (equal variances) table from the Select Test Design & Goal window.
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.
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Step 2:
Enter the values for sample size calculation taken from the study design statement and survival parameter converter.
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Step 3:
Once the relevant Power is entered in the power row, the sample size is calculated automatically.
| This gives a sample size of 235, as per the study design |
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In the case of the ANCOVA analysis used in the study, the only additional information necessary would be an estimate of R2 between the response and the covariates. For example, using the ANCOVA sample size table available in nQuery Advanced for the above study and assuming a 10% R2 between baseline and the response would have yielded an adjusted sample size of 211 per group.
Step 4:
Once the calculation is completed, nQuery Advanced provides an output statement summarizing the results. It States:
| Output Statement: |
|
A sample size of 235 in each group will have 90% power to detect a difference in means of 0.6 assuming that the common standard deviation is 2 using a two group t-test with a 5% two-sided significance level. |
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