Accuracy
Definition
The degree to which a measured value agrees with the accepted true or reference value of the quantity. A biased instrument can produce precise but inaccurate results. Accuracy is assessed using certified reference materials or standards with known values.
- Definition
- Closeness of a measured value to the true value
- Contrast
- Precise results can still be biased and inaccurate
- Assessment tool
- Certified reference materials (CRMs)
- Field
- Analytical measurement quality
Common questions
How can an instrument be precise but still inaccurate?+
A systematic bias, such as miscalibration, shifts every reading by the same amount, so repeated measurements cluster tightly together yet consistently miss the true value.
Why are certified reference materials used to assess accuracy?+
A CRM has an assigned value determined by an accredited process with a known uncertainty, giving a trustworthy benchmark to compare measured results against.
Can a method be accurate on average without being precise?+
In principle, if random errors cancel out over many measurements, but low precision makes any single result unreliable even when the long-run average is accurate, so both properties are checked together.
Related terms
- Between-Class Variability
- The spread of measurements between items from different sources or categories. A forensic method is most discriminating when between-class variability is large...
- Measurement Error
- The discrepancy between a recorded value and the true value of the property being measured. Arises from instrument calibration limits, analyst technique,...
- Precision
- The degree to which repeated measurements of the same specimen under the same conditions agree with each other. Quantified by the standard...
- Repeatability
- The agreement between successive measurements of the same specimen made by the same analyst, on the same instrument, in the same laboratory,...
- Within-Class Variability
- The natural spread of measurements among items that share a common source, class, or category. For example, the range of refractive index...