Specialty › Precision & CI width

CV from duplicates

Precision-based sizing finds how many paired duplicates are needed to estimate a coefficient of variation to a target relative half-width, from 95% CI ≈ CV · z / √(2n).

What is CV from duplicates?

When the precision target is on CV (relative variability rather than absolute), the formula scales with CV² rather than σ² — both because CV is what you're estimating and because its SE depends on CV.

When should I use CV from duplicates?

  • Analytical-method precision validation.
  • Establishing the n for a duplicate-measurement reliability study.

What data does it need?

Expected CV + target relative half-width.

What does it report?

Required number of duplicate pairs.

How do I interpret the result?

A typical analytical-method CV of 5% needs ~40 paired duplicates for a 25%-relative half-width CI on the CV — small studies fail to pin the CV down precisely.

See also