Is my treatment different from my control?
Compare two groups
Choosing and running a two-group comparison, and reporting it usefully.
The default is an unpaired t-test, and Welch’s version of it should be your standard rather than the equal-variance one — it costs almost nothing when variances match and saves you when they do not. Use a paired test only when each measurement genuinely has a partner: the same dish before and after, the same animal on both days. If your data are clearly not normal and n is small, Mann–Whitney is the usual fallback, though with very small n it has little power to detect anything.
The larger point is what you report. A p-value tells you almost nothing on its own. Give the difference between means and its confidence interval, and show the individual points. An estimation plot does all three at once.
If you measured several dishes from each of three independent experiments, your n is three, not the number of dishes. Pooling technical replicates as though they were independent is the single most common way biology papers report significance that is not there.
What to use
- t-test calculator
Compare two groups and get the effect size and interval, not just a p-value.
Built inNo upload - estimationstats.com
Estimation plots: effect size with confidence interval, not just a p-value.
ExternalHo, Tumkaya et al.Free - jamovi
Free point-and-click statistics built on R, with a spreadsheet front end.
Externaljamovi projectDesktop install - GraphPad Prism
The default statistics and graphing package in experimental biology.
ExternalDotmaticsPaid - 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.