Cohort Study Sample Size

20%
10%
80%

Results will appear here

Enter the expected risks in both groups and study parameters to calculate the required sample size.

Formula

Sample Size for Cohort Studies

n=(ZΞ±/22pΛ‰(1βˆ’pΛ‰)+ZΞ²p1(1βˆ’p1)+p2(1βˆ’p2))2(p1βˆ’p2)2n = \frac{\left(Z_{\alpha/2}\sqrt{2\bar{p}(1-\bar{p})} + Z_{\beta}\sqrt{p_1(1-p_1) + p_2(1-p_2)}\right)^2}{(p_1 - p_2)^2}

Where:

  • n = sample size per group
  • p1p_1 = risk in exposed group
  • p2p_2 = risk in unexposed group
  • pΛ‰\bar{p} = (p1+p2)/2(p_1 + p_2)/2 (pooled proportion)
  • ZΞ±/2Z_{\alpha/2} = Z-score for significance level
  • ZΞ²Z_{\beta} = Z-score for power