Sample Size Calculation Proportion Formula

Sample size calculation for a proportion is crucial in ensuring your study has enough participants to detect a significant difference between groups. Here’s why it matters…

1. Select your desired confidence level and power.
2. Enter the expected proportion.
3. Click ‘Calculate’.

The formula used is: n = (Z_α/2 + Z_β)² * p * (1 – p) / (p1 – p)²

Comparison of Sample Sizes for Different Confidence Levels

Confidence Level	Sample Size
90%	64
95%	129
99%	661

• Always round up to the nearest whole number.
• Consider using a sample size calculator for complex scenarios.

What is the difference between confidence level and power?

Confidence level is the probability that the calculated interval contains the true population parameter, while power is the probability of detecting a significant effect when there is one.

CDC’s guide on sample size and Statistics How To’s sample size calculator are excellent resources.