2.3 Performance Characteristics

Some of the common terms used in defining the performance of a method are:

• Accuracy

• Bias

• Conventional true value

• Detection limit

• Discriminate

• Discrimination threshold

• Instrument parameters

• Intermediate precision

• Limit of detection

• Limit of quantitation

• Linearity

• Precision

• Range

• Recovery

• Repeatability

• Repeatability conditions

• Repeatability limit

• Repeatability standard deviation

• Reproducibility

• Reproducibility conditions

• Reproducibility limit

• Robustness

• Ruggedness

• Scope

• Selectivity

• Sensitivity

• Signal-to-noise ratio

For the results of an analysis to be of use to a client, the analytical measurements need to be fit for the purpose for which they were intended. Key measures for determining the appropriateness of the analytical method used by a laboratory include bias, accuracy and precision.

If it is found that a method consistently produces higher (or lower) results for the analysis of a substance of known composition, the method is said to be biased.

The bias of a measurement result is defined as a consistent difference between the measured value and the true value. In mathematical terms it is the systematic component of measurement error.

The bias is a measure of the difference between a mean value of a set of results and a stated value ( e.g. Certified Reference Material, Section 3.1).

Accuracy is often used instead of bias and trueness. It can be seen from Figure 2 that it involves bias and precision.

Figure 2: Bias of measurement results