Precision, Repeatability, and Reproducibility

Precision: In the context of repeatability and reproducibility, precision is the closeness of agreement between independent measurements of a quantity under the same conditions.

Since precision is not based on a "true" value, there is no bias or systematic error in the value. Rather it is dependent on the distribution of random errors.

Repeatability: Repeatability conditions include:
• the same measurement procedure
• the same observer
• the same instrumentation, under the same conditions
• the same location
• repetition over a "short" period of time
The precision determined when the same methods and equipment, used by the same operator, under identical conditions are used to make multiple measurements on identical specimens.

Reproducibiity: A valid statement of reproducibility requires a list of the conditions that have changed. Changed conditions may include:
• principle of measurement
• method of measurement
• observer
• measuring instrument
• reference standard
• location
• conditions of use
• time
The precision determined when the same methods, but different equipment and operators are used to make measurements on identical specimens.

Accuracy and Error

Error is the difference between the true value and the measured value. The total error is a combination of systematic error and random error.

Trueness is largely affected by systematic error.

Precision is largely affected by random error.

Accuracy is an expression of the lack of error (i.e., defined by the certainty of the measurement).


See Also: Accuracy and Precision, Accuracy, Trueness, and Precision