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8 Measurement Uncertainty
the assigned uncertainty of the measurement is the confirmation of its reliability,
hence the effort involved in the evaluation of the measurement uncertainty is fully
justified substantively.
The result of the measurement can be considered reliable only when it is provided with an assigned uncertainty determined in accordance with the procedure described in the ISO GUM guide.
As previously mentioned, the evaluation of the measurement uncertainty is a
rational process of evaluating its reliability. Hence an increasing number of laboratories conducting chemical measurements pay attention to that issue. The process
of evaluation of the uncertainty requires the analyst to critically estimate all steps
of the measuring procedure that can be the source of the uncertainty and can have
a significant impact on the measurement result. For the end-users of the results,
the value of the uncertainty shows the range in which the result can be reliable. It
should be clearly emphasized that a correctly conducted evaluation of the uncertainty
allows the measuring procedure used to be critically assessed. Providing a result with
assigned uncertainty is extremely important when results are compared, especially
when decisions made on that basis relate to levels in the area close to the limiting
values (e.g., the highest acceptable concentration of a given substance).
To summarize the above considerations, it can be said that the ability to correctly
calculate the result uncertainty becomes an indispensable tool in the everyday work
of the analyst. The correctly evaluated values of the uncertainty are also indispensable in determining the cohesion of the measurements. As previously mentioned,
the commonly accepted procedure for calculating uncertainty is the one described
in the GUM guide. Issued by the ISO, the Guide to the Expression of Uncertainty
in Measurement (ISO GUM) defines the generally accepted process of calculating
and expressing uncertainty in different types of measurements. According to the
described guidelines, the procedure includes the identification of potential factors
that influence the measurement result, the determination (on the basis of own experimental data or on the basis of literature) of their numerical values, the consideration
of the source of uncertainty and calculation of the value of the combined standard
uncertainty and then of the expanded uncertainty. The procedure uses appropriate
mathematical (statistical) tools that enables the inclusion of various factors that influence the result. Thanks to that, it is possible to obtain a numerical value (uncertainty)
including all previous measurement results, current experimental data, information
from the manufacturer of the equipment or standards and literature data. Remember
that providing the result with an assigned uncertainty does not mean that the value
of the uncertainty must be small.
It is worth quoting a statement here from the ISO GUM guide § 3.4.8:
8 Measurement Uncertainty
the assigned uncertainty of the measurement is the confirmation of its reliability,
hence the effort involved in the evaluation of the measurement uncertainty is fully
justified substantively.
The result of the measurement can be considered reliable only when it is provided with an assigned uncertainty determined in accordance with the procedure described in the ISO GUM guide.
As previously mentioned, the evaluation of the measurement uncertainty is a
rational process of evaluating its reliability. Hence an increasing number of laboratories conducting chemical measurements pay attention to that issue. The process
of evaluation of the uncertainty requires the analyst to critically estimate all steps
of the measuring procedure that can be the source of the uncertainty and can have
a significant impact on the measurement result. For the end-users of the results,
the value of the uncertainty shows the range in which the result can be reliable. It
should be clearly emphasized that a correctly conducted evaluation of the uncertainty
allows the measuring procedure used to be critically assessed. Providing a result with
assigned uncertainty is extremely important when results are compared, especially
when decisions made on that basis relate to levels in the area close to the limiting
values (e.g., the highest acceptable concentration of a given substance).
To summarize the above considerations, it can be said that the ability to correctly
calculate the result uncertainty becomes an indispensable tool in the everyday work
of the analyst. The correctly evaluated values of the uncertainty are also indispensable in determining the cohesion of the measurements. As previously mentioned,
the commonly accepted procedure for calculating uncertainty is the one described
in the GUM guide. Issued by the ISO, the Guide to the Expression of Uncertainty
in Measurement (ISO GUM) defines the generally accepted process of calculating
and expressing uncertainty in different types of measurements. According to the
described guidelines, the procedure includes the identification of potential factors
that influence the measurement result, the determination (on the basis of own experimental data or on the basis of literature) of their numerical values, the consideration
of the source of uncertainty and calculation of the value of the combined standard
uncertainty and then of the expanded uncertainty. The procedure uses appropriate
mathematical (statistical) tools that enables the inclusion of various factors that influence the result. Thanks to that, it is possible to obtain a numerical value (uncertainty)
including all previous measurement results, current experimental data, information
from the manufacturer of the equipment or standards and literature data. Remember
that providing the result with an assigned uncertainty does not mean that the value
of the uncertainty must be small.
It is worth quoting a statement here from the ISO GUM guide § 3.4.8: