• Uncertainty - a parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the quantity being measured.

• Type A evaluation of uncertainty - quantification of uncertainty component using statistical methods.

• Type B evaluation - quantification of uncertainty component using non-statistical methods.

• Standard uncertainty - standard deviation associated with a single component of uncertainty.

• Sensitivity coefficient - coefficient showing the relationship between a single uncertainty component and the standard deviation of a result.

• Combined standard uncertainty - standard deviation associated with the result of a particular measurement or series of measurements that takes into account one or more components of uncertainty.

• Expanded uncertainty - combined standard uncertainty multiplied by an appropriate critical value from the t-distribution which depends upon the degrees of freedom in the combined standard uncertainty and the desired level of coverage.

• Effective degrees of freedom - degrees of freedom associated with a standard deviation composed of two or more components of variance and computed using the Welch-Satterthwaite approximation.

• Level-1 standard deviation - repeatability standard deviation describing the distribution of short-term measurements under repeatability conditions.

• Level-2 standard deviation - standard deviation describing the distribution of measurement results over intermediate time-intervals such as day-to-day.

Note - this standard deviation is a function of the between-day standard deviation and the repeatability standard deviation.

• Level-3 standard deviation - standard deviation describing the distribution of measurement results over the long-term such as run-to-run.

Note - this standard deviation is a function of the between-run standard deviation, the between-day standard deviation and the repeatability standard deviation.

• Between-day standard deviation - standard deviation describing the distribution of intermediate-term (day-to-day) fluctuations in the measurement process.

• Between-run standard deviation - standard deviation describing the distribution of long-term (run-to-run) fluctuations in the measurement process.

Normative references for this document are:

• ISO 3534-Part 1: General vocabulary

• ISO 3435-Part 2: Statistical terms

• ISO 3435-Part 3: Design of experiments

• ISO 5725-Part 1: Accuracy of measurement methods and results: General principles and definitions

• ISO 5725-Part 2: Accuracy of measurement methods and results: Basic method for the determination of repeatability and reproducibility of a standard measurement method

• ISO 5725-Part 3: Accuracy of measurement methods and results: Intermediate measures of precision of a standard measurement method

• ISO 5725-Part 4: Accuracy of measurement methods and results: Basic methods for the determination of trueness of a standard measurement method

• ISO 5725-Part 5: Accuracy of measurement methods and results: Alternative methods for the determination of the precision of a standard measurement method

• ISO 5725-Part 6: Accuracy of measurement methods and results: Use in practice of accuracy values

ISO 11095: Linear calibration using reference materials