PHARM/PCS V5 · Procedure 41 Pairwise and Nonparametric
Ratio of Means
Put honest confidence limits on the ratio of two means with Fieller's theorem, for fold-changes, relative bioavailability, or potency.
What it computes
Computes asymmetric confidence limits for the ratio of two independent means using Fieller's theorem.
Inputs and outputs
You provide
- The values for each of the two groups, entered as two blocks
- A confidence level
PHARM/PCS reports
- The ratio of the two means
- Its asymmetric confidence limits
When to use it
When your result is naturally a ratio of two measured means and you need honest confidence limits: potency ratios, relative bioavailability, fold-changes. It's the same method behind the potency-ratio limits in Procedure 11, generalized to any ratio.
Reading the results
Ratios have asymmetric, sometimes unbounded confidence limits; when the denominator mean isn't clearly different from zero, the interval can open to infinity, which is Fieller's honest signal that the ratio is poorly determined. Don't replace these with a naive symmetric interval, which would understate the uncertainty.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.