Precision vs Accuracy: What the Difference Means for Results¶
"Precise" and "accurate" are often used interchangeably — but in assay validation they mean different things, and an assay can be one without the other. This page explains the distinction.
The Bullseye Analogy¶
| Concept | Analogy | Assay metric |
|---|---|---|
| Precision | Arrows grouped tightly (regardless of bullseye) | CV% (coefficient of variation) |
| Accuracy | Arrows near the bullseye | Correlation vs reference (r), bias |
- Precise but inaccurate = consistently wrong (tight group, wrong target).
- Accurate but imprecise = right on average, but scattered.
Precision (CV%)¶
Precision measures repeatability — how much repeated measurements of the same sample vary.
| CV% | Interpretation |
|---|---|
| < 8% | Excellent |
| 8–15% | Acceptable for quantitative POCT |
| > 15% | Poor — results fluctuate meaningfully |
For a patient monitored over days, low CV% is essential: otherwise you cannot separate a real patient change from measurement noise.
Accuracy (Correlation & Bias)¶
Accuracy measures correctness — how close the result is to the true value.
| Metric | What it measures |
|---|---|
| Correlation (r) | Agreement with a reference method (r > 0.95 target) |
| Bias | Systematic difference from the true value (< 10% target) |
Why Both Are Validated¶
An assay must be both precise and accurate. Precision alone means consistent-but-wrong; accuracy alone means right-on-average-but-unreliable. Migibio validates both for every assay.
FAQ¶
Can an assay be precise but inaccurate? Yes — a consistent systematic error (e.g., a miscalibrated curve) produces tight but wrong results. This is why accuracy validation against a reference method is essential.
Which matters more for patient monitoring? Precision — because monitoring compares values over time, and low precision would obscure real changes.
For the full validation framework, see Validation Methodology.
Authored by: Migibio Clinical & Scientific Affairs, Guangzhou Magic Biotech Co., Ltd.
Reviewed by: Migibio R&D Quality Committee
Last updated: 2026-08-13
Disclosure: Migibio (Guangzhou Magic Biotech Co., Ltd.) is the manufacturer of the FIA680/FIA880 analyzers and FICT reagents referenced in this content. See our Editorial & Review Policy.