Does one measurement predict the other?
Test whether two variables are related
Correlation, linear regression, and the difference between them.
Correlation asks whether two variables move together and treats them symmetrically. Regression asks how much one changes per unit of the other, and assumes you know which is the predictor. If you cannot say which variable causes which, you want correlation.
Pearson’s r assumes a linear relationship and reasonably normal data; Spearman’s rho works on ranks and handles curves and outliers. Always plot the data first — Anscombe’s quartet is four datasets with identical correlation coefficients and entirely different shapes.
R² describes how well the line fits the data you have. It says nothing about whether the relationship is causal, and nothing about whether it holds outside the range you measured.
What to use
- Correlation and regression
Pearson or Spearman with a confidence interval on r, plus a fitted line.
Built inNo upload - GraphPad Prism
The default statistics and graphing package in experimental biology.
ExternalDotmaticsPaid - jamovi
Free point-and-click statistics built on R, with a spreadsheet front end.
Externaljamovi projectDesktop install - R and RStudio
The statistical environment nearly all biological methods are written for.
ExternalR Foundation / PositFree
If you script
Command-line and library options. No page here — they need an environment rather than a browser.
- statsmodelsPython package
Statistical models and hypothesis tests for Python.