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Gum Bottom up and Top down Approaches – the Best Method to Perform
Measurement uncertainty is a metrological concept to quantify the variability
of measurement results. “Bottom up approach” based on a comprehensive
mathematical model of the measurement procedure, evaluating individual
uncertainty contribution as dedicated input quantities. It was acknowledged
as the master document on the subject of measurement uncertainty. The
advantages of bottom up approaches are demanding critical assessment and
full understanding of the analytical steps in a test method, consistent with
other fields of measurements such as calibration, the MU result generated is
relevant to the particular laboratory that produces it.
The top down approach is based on using the performance parameters of
collaboratively studied reference methods. Top up approach”, based on
whole method performance to comprise the effects from as many relevant
uncertainty sources as possible using the method bias and precision data.
Such approaches are fully in compliance with the GUM, provided that the
GUM principles are observed. There are few alternative top down
approaches, receiving greater attention from the global testing community
today. Top down approaches consider mainly Type A data from own
statistical analysis from within lab method validation and inter laboratory
comparison studies. The top down approach allow for method bias in
uncertainty budget. The top down approach strategy combines the use of
existing data from validation studies with the flexibility of additional modelbased evaluation of individual residual effect uncertainty contributions. The
advantages of top down approaches are Quality data from method validation
and inter-lab comparison studies are readily available in a well run
accredited laboratory, Very much simpler process in MU evaluation, The MU
data of a test method is dynamic and current, due to using existing and
experimentally determined quality control checks and method validation
results, the MU data of a test method is dynamic and current, due to using
existing and experimentally determined quality control checks and method
The significant sources of GUM bottom up and top down approaches is
used for evaluating the uncertainty. Valuable techniques are used in the
evaluation of test validity approaches. In this contribution, the top-down
evaluation of uncertainty derived from the participation of inter comparison
rounds and proficiency testing schemes will be presented. Here, the results
will be compared with the bottom-up evaluation of uncertainty, and ease of
applicability, validity and usefulness of both approaches will be discussed.