Sample Size Calculator For Comparing 2 Independent Proportions

Sample size calculation is crucial in comparing two independent proportions. It ensures that your study has enough participants to detect a meaningful difference between the two groups.

1. Select the significance level (α).
2. Enter the desired power (1 – β).
3. Enter the proportions for the two groups (p1 and p2).
4. Click “Calculate”.

The calculator uses the following formula to calculate the sample size:

n = (Z_α/2 + Z_β)² * (p1 * (1 – p1) + p2 * (1 – p2)) / (p1 – p2)²

Sample Sizes for Different Power Levels

Power (1 – β)	Sample Size (n)
0.8	78.4
0.9	109.5

• Always round up the calculated sample size to the nearest whole number.
• Consider using a software tool for complex calculations.

What is the significance level (α)?

The significance level (α) is the probability of rejecting the null hypothesis when it is true. It is typically set at 0.05.

For more information, see the CDC’s guide on sample size calculation and the UNC’s sample size calculation guide.