Brief Outline of Measurement Uncertainty

The parameter could be standard deviation or width of a confidence interval. 

In analytical sciences, measurement uncertainty narrows down the differences between the actual measured value and the true value of a concentration of analyte. The actual measured value consists of two parts, the estimate of the true value and uncertainty associated with this estimation. Uncertainty of measurement is made of every component that is critical to the measured value, some of which may be evaluated from statistical distribution of the results of a series of measurements and can be characterised by standard deviations. The actual measured value does not coincide with the true value and may be considered as an estimate that may be larger or smaller than the true value. This is not an error but rather an inherent part of any measurement. Hence it is true to state that  

Determination of measurement uncertainty must be carried out with accepted and recognised methods that have already been validated and these methods are intrinsically tied to all possible errors in the method. 

A measured value is complete only when it is accompanied by a statement of its uncertainty and is required in order to decide whether or not the result is adequate for its intended purpose. The uncertainty value must be suitably small to show that the reported results can be accepted with confidence and to ascertain whether or not it is consistent with similar results. There is an uncertainty in the concentration of the calibration samples used both in synthetic calibration samples and calibrations of standard addition. Weighing and volumes, which are a must in most analytical methods, must include weighing errors volumes must include volume errors to take into account uncertainties associated with these steps of the analysis. These and others must also be included in the overall calculation of the analytical error. 

It is important to note the differences between error and measurement uncertainty. Errors are differences in measurements while uncertainties are a range of measurement. The importance of measured uncertainty values quoted with the results improves the reliability of a result and adds confidence in the decision and reporting of the same. Knowledge of the uncertainty value also give credence to strive to reduce the uncertainty value associated with measurements which will facilitate better and more confident reporting. 

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