How It Works
Study Design
Short-term and long-term precision are routinely assessed in both verification and validation. Choose the design that matches the sources of variability you need to characterize:
| Purpose | Rapid assessment of within-run repeatability |
| Run structure | Single run or continuous run |
| Replicates | Typically 10–20 replicates in one run |
| Concentration levels | Multiple levels recommended (e.g. low and high); each level evaluated independently |
| Precision type | Repeatability (within-run) only — does not capture between-run or between-day variation |
| Comparison | Observed SD vs. Goal SD (derived from TEa) or manufacturer claim |
Because all replicates are collected in a single run, Simple Precision measures only within-run repeatability. Use a Complex (multi-day) design when between-run or between-day sources of variability must be estimated.
| Days | 5 minimum |
| Runs per day | 1 run per day |
| Replicates per run | 5 replicates per run |
| Concentration levels | 2 levels recommended (low and high) |
| Total measurements | 25 per concentration level (minimum) |
The 5 × 1 × 5 design yields a degrees-of-freedom for repeatability (dfR) of 20 — the minimum EP15-A3 requires for a statistically valid short-term assessment. Calculates within-run (repeatability) and within-laboratory (total) precision. Used in both verification and validation contexts when a short multi-day protocol is appropriate.
| Days | 20 days |
| Runs per day | 2 runs per day |
| Replicates per run | 2 replicates per run |
| Concentration levels | At least 2 levels recommended |
| Total measurements | 80 per concentration level |
The 20 × 2 × 2 design captures within-run, between-run, between-day, and within-laboratory variance components via ANOVA. The two-run-per-day structure is essential for separating between-run from between-day sources of variability. Used in both verification and validation when long-term precision components must be characterized.