Measurement uncertainty reporting

Note that overall measurement uncertainty did not exceed 6% for glucose and potassium determinations. For Ca the overall measurement uncertainty did not exceed 2.5% and for urea 13%. These values closely agree with measurement uncertainties reported for dif-... 

Uncertainty expresses the range of possible values that a measurement or result might reasonably be expected to have. Note that this definition of uncertainty is not the same as that for precision. The precision of an analysis, whether reported as a range or a standard deviation, is calculated from experimental data and provides an estimation of indeterminate error affecting measurements. Uncertainty accounts for all errors, both determinate and indeterminate, that might affect our result. Although we always try to correct determinate errors, the correction itself is subject to random effects or indeterminate errors. 

The Thermodynamics Research Center staff have assigned an uncertainty value to each observed and recommended density value listed in the tables. The tme value of the property has a 95% probability of being in the range covered by + or - the uncertainty about the reported value. Assignment of uncertainty is a subjective evaluation based upon what is known about the measurement when the value is entered into the database, and includes the effects of all sources of experimental error. The errors have been propagated to the listed density at the reported temperature. Uncertainties reported by the investigators are considered but not necessarily adopted. Often, investigators report repeatability, but they usually do not provide uncertainty. 

The r2 is but 0.998 with a standard deviation of ca 1.0 kJ mol 1 (Figure 2). Again the diphenyl species 129 is sorely deviant, this time above the line by some 59 kJmol-1, i.e. in the opposite direction. Despite the nearly 15 kJ mol 1 uncertainty reported for the measurement for enthalpy of formation of diphenylfulvene, these results suggest the... 

Do you normally give a measurement uncertainty/reliability when reporting results to your customer ... 

Otherwise there will be a tendency among some laboratories to report unrealistic low measurement uncertainties... 

If we report the measurement uncertainty to our customer we always have to state also the level of confidence of the range we report as uncertainty. Otherwise the uncertainty statement is completely useless. It could be helpM, also to state the method that was used to estimate the uncertainty. 

NORDTEST Hanctiookfor calculation of measurement uncertainty in environmental laboratories Report TR 537 (www.nordicinnavation.net/nadtest ctm)... 

Measurement uncertainty is increasingly gaining attention, in particular in the framework of accreditation. The new accreditation standard ISO/IEC 17025 [17], which has been in force from December 2002 on, contains clear requirements on the estimation of MU and when and how it should be stated in test reports. ISO/IEC 17025 requires MU to be reported when required by the client and when relevant to the application and interpretation of the measurement results in the framework of certain specifications or decision limits. The MU should be readily available and reported together with the result as X U, where U is the expanded uncertainty [17, 47, 51, 54]. Also Eurachem and CCMAS within the Codex Alimentarius deal with MU as a separate issue [14,18-20]. Some even claim that MU will become the main unifying principle of analytical data quality [37]. 

Of importance to the traceability of the results is a proper estimate of the measurement uncertainty of each participant. The error bars in figure 5.7 are the expanded uncertainties reported by the laboratories, in some cases with a coverage factor relating to more appropriate degrees of freedom. Table... 

The International Vocabulary of Basic and General Terms in Metrology (VIM), second edition (ISO 1993a), defines uncertainty of measurement as the parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand (term 3.9). In the third edition (Joint Committee for Guides in Metrology 2007), the term measurement uncertainty is defined (term 2.27), and reasonably attributed is replaced by attributed to a measurand based on the information used. This definition emphasizes that the estimate of uncertainty is only as good as the information used to calculate it, so a report of an uncertainty should also state what information was used to calculate the uncertainty. 

Section 5.4 of the ISO/IEC standard 17025 (ISO/IEC 2005) requires Testing laboratories shall have and shall apply a procedure to estimate the uncertainty of measurement, and in a test report where applicable, a statement on the estimated uncertainty of measurement information on uncertainty is needed in test reports when it is relevant to the validity or application of the test results, when a client s instruction so requires, or when the uncertainty affects compliance to specification limits (ISO/IEC 2005, section 5.10). Although the reporting clause leaves open the possibility of not including the measurement uncertainty of a result, I believe that the added value to the client of a proper measurement uncertainty statement far outweighs any temporary problems that may be caused by unfamiliarity with the measurement uncertainty concept. 

There are apocryphal stories of a statement of measurement uncertainty in a test report being used court and eliciting questions from defense counsel... 

The top-down approach is often used when there are method validation data from properly conducted interlaboratory studies, and when the laboratory using reproducibility as the measurement uncertainty can demonstrate that such data are applicable to its operations. Chapter 5 describes these types of studies in greater detail. In assigning the reproducibility standard deviation, sR, to the measurement uncertainty from method validation of a standard method, it is assumed that usual laboratory variables (mass, volume, temperature, times, pH) are within normal limits (e.g., 2°C for temperature, 5% for timing of steps, 0.05 for pH). Clause 5.4.6.2 in ISO/ 17025 (ISO/IEC 2005) reads, In those cases where a well-recognized test method specifies limits to the values of the major sources of uncertainty of measurement and specifies the form of presentation of the calculated results, the laboratory is considered to have satisfied this clause by following the test method and reporting instructions. ... 

NCRP (1997). National Council on Radiation Protection and Measurements. Uncertainties in Fatal Cancer Risk Estimates Used in Radiation Protection, NCRP Report No. 126 (National Council on Radiation Protection and Measurements, Bethesda, Maryland). 

Of the 14 participants, only labs 2, 6, 9, 10 and 16 have reported a result that agrees with the assigned value (within the respective measurement uncertainties). 

In presentation and interpretation of results, NARL aims for objectivity, clear presentation, and statistical data treatment that is transparent to participants, internationally accepted and metrologically sound. Sources of chemical standards, statements concerning traceability and estimates of measurement uncertainty are included in the study report. 

The participants were told the nominal concentration of the cylinders they received, but not the absolute value. The results of these analyses were returned to NP.U. Participants were given the option to report the measurement uncertainty that they assigned to the results obtained. Not all participants took part in all tests and very few reported uncertainties. 

Setting Criteria for Acceptable Reported Measurement Uncertainties in IMEP... 

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