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Estimating Sample-Size Requirements with a Handy Calculator

While many programs, apps, and web pages are available to perform power and sample-size calculations, they aren’t always easy or intuitive to use. Because spreadsheets like Excel are readily available and intuitive, it’s convenient to have a single spreadsheet that can perform power and sample-size calculations for the situations that arise most frequently in biological and clinical research.

The Sample Size Calculations spreadsheet gives you a simple way to estimate the sample size you need when designing a study involving the following statistical analyses:

Click here for two-group (unpaired) comparison of means by the Student t test.

Click here for two-group (paired) comparison by the Student t test.

Click here for comparison of two observed proportions by the chi-square or Fisher Exact test.

Click here for comparison of one observed proportion versus a fixed proportion value.

Click here for test for correlation coefficient = 0.

Click here for one-way ANOVA for balanced (equal-sized) groups.

Click here for comparison of two event rates.

Click here for survival analysis by log-rank or Cox proportional-hazards regression.

It’s important to realize that most of the calculations in this spreadsheet are only approximations. They’ll usually give sample-size answers that are within a few subjects of the exact answer, which should be adequate when you’re planning a study. But they shouldn’t be taken as the “official” answers.

Before you use the calculator for any of the preceding calculations,

Click here for a few basic instructions and concepts.

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