Accuracy and Precision

Accuracy and Inaccuracy

The accuracy of a measurement is how close a result comes to the true value.

Systematic error or Inaccuracy is quantified by the average difference (bias) between a set of measurements obtained with the test method with a reference value or values obtained with a reference method.

Precision and Imprecision

Precision refers to how well measurements agree with each other in multiple tests.

Random error or Imprecision is usually quantified by calculating the coefficient of variation from the results of a set of duplicate measurements (Westgard, 2008).

Graphical representation

Accurate and Precise		Accurate but not Precise
Precise but not Accurate		Not Precise or Accurate

Literature

• Westgard JO (2008) Basic method validation. 3^rd ed. Madison: Westgard QC, Inc.

See also

• Concordance correlation coefficient