Accuracy and Precision

Accuracy and Inaccuracy

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

Systemetic 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.

Inaccuracy and Imprecision

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
Accurate and Precise

 

Accurate but not Precise

 

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

 

Literature

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

See also