Repeatability precision study

ICH Q2(R2) describes precision at three levels. Repeatability is the precision under the same conditions over a short interval: one analyst, one instrument, one day. Intermediate precision adds the variation within a laboratory — different days, analysts or equipment. Reproducibility is the precision between laboratories. This page assesses repeatability only; the other two need a grouped design and an analysis of variance, and are not computed here.

The guideline asks for a minimum of nine determinations covering the range (three concentrations, three replicates each) or six determinations at 100 % of the test concentration. Enter one such set per study; the standard deviation, the relative standard deviation and the confidence interval on the mean come from the same replicate engine as the free calculator, with the two-sided Student's t taken from a tabulated lookup rather than an approximation.

The conventional assay default is a %RSD of at most 2 % — a figure the guideline leaves to the study protocol, and one that trace-level or bioanalytical methods routinely set higher. The verdict here uses that default with an inclusive bound, so a study landing exactly on 2.0 % meets it. AOAC states no default repeatability criterion; under that guideline the protocol supplies one and the card says so.