Learn more with dummies

Enter your email to join our mailing list for FREE content right to your inbox. Easy!

Estimating Sample Size for Correlation Tests in Biostatistics

By John Pezzullo

Part of Biostatistics For Dummies Cheat Sheet

For a correlation test in biostatistics (such as the Pearson or Spearman test), pick the scatter chart that looks like an important amount of correlation. Each chart shows the value of r (the correlation coefficient) and the required number of analyzable subjects (each providing an x and a y value). For example, if the scatter chart in the lower left corner (corresponding to r = 0.6) appears to show an important amount of correlation, you’ll need about 20 analyzable subjects.

[Credit: Illustration by Wiley, Composition Services Graphics]

Credit: Illustration by Wiley, Composition Services Graphics

For other r values that aren’t in the preceding scatter charts, use this rule of thumb to estimate sample size: You need about 8/r2 – 3 analyzable subjects.