Precision (metrology)

Precision is the closeness of agreement among repeated measurements under specified conditions. It describes measurement consistency, not closeness to a true or accepted value.

Accuracy and precision: Accuracy is closeness to a true or accepted value; precision is closeness among repeated measurements. The distinction prevents consistent measurements from being mistaken for accurate ones.
Standard deviation: A statistic measuring the spread of values around their mean. It is a common numerical expression of precision for repeated measurements.
Analytical precision: The closeness of agreement among repeated results from an analytical measurement procedure. It applies precision assessment to laboratory methods and reported analytical results.
Bias (statistics): A systematic difference between an estimator's expected value and the quantity it estimates. A measurement series can be precise yet biased away from the reference.
Trueness: Trueness is the closeness of a measurement average to a reference value. It captures the systematic component of accuracy that precision does not describe.
Variance: The mean squared deviation of values from their mean. It quantifies measurement dispersion in squared units and underlies standard deviation.
Interlaboratory study: A coordinated comparison in which multiple laboratories measure shared materials or samples. Between-laboratory agreement estimates precision across broader conditions.
Random error: Unpredictable variation in measured values that causes repeated results to differ. Random error is a major source of limited precision.
Repeatability: Measurement precision under the same procedure, operator, instrument, location, and short time interval. It is precision assessed under the most tightly controlled set of conditions.
Coefficient of variation: The ratio of a standard deviation to a mean, often expressed as a percentage. It compares relative precision across measurements with different scales.

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