Uncertainty of measurement, also known as measurement uncertainty (MU) expresses the variability in the measurement process. It qualifies the accuracy of the result, providing the customer with sufficient information to be able to interpret the measurement to make an informed decision about what the measurement represents. Statistically, it is an interval associated with a measurement which expresses the range of values that can reasonably be attributed to the quantity being measured.

How does Affinity Labs determine and report UOM?

As a NATA accredited laboratory, Affinity Labs must identify and consider all the components that contribute to the variability of the measurement process and then estimate those contributions that significantly impact the measurement result using multiple statistical calculations. All of this culminates in what is called an expanded MU. This expanded MU provides an estimate of the range of values that could reasonably represent the true value within a stated coverage probability or level of confidence.

Affinity Labs estimates MU using reproducibility data accumulated from initial method validation to provide the statistical measurements for mean, standard deviation (SD) and Coefficient of Variation (CV) for the analyte of interest. The expanded uncertainty is then calculated using the coverage factor of 2 using the SD (absolute uncertainty) or CV (relative % uncertainty). This coverage factor of 2 gives a corresponding level of confidence of 95%.

In some cases two different levels of UOM may be applied to an analyte having a large range of numerical results. See the example below:

Analyte A        
Range 5 – 80 mg/L     UOM (95% CI) = 2 x SD = ± 4 mg/L
Range > 80 mg/L        UOM (95% CI)  = 2 x CV = ± 10 %

Does UOM change?

Affinity Labs regularly reviews UOM using Quality Control (QC) data accumulated via our Quality System.

Sometimes this may result in a change of the UOM for a particular analyte, therefore it is important to access the most current version of the UOM documents.

Affinity Labs uncertainty of measurement documents

The current versions of UOM documents can be accessed using the links below.

Uncertainty of Measurement for Trace Laboratory Methods

Uncertainty of Measurement for Analytical Laboratory Methods