Consensus mean

Post-hoc consensus does not independently establish the value of the measurand, and although it provides internal consistency, comparison with other testing rounds and proficiency tests should be made with care. In some cases the outliers from the consensus mean in a round may be the only ones with the correct answer. When an empirical method is used to establish the assigned value, this method should be made known to the participants in advance. Where the assigned value is provided with an uncertainty (as it would be in cases 1-3 above), the uncertainty should be small compared to... 

Attempts to correlate analytical performance with other seemingly indicative laboratory characteristics, such as participation in proficiency testing schemes, regular use of certified RMs, number of years of experience and number of samples analysed per year were all equally unsuccessful. Therefore, in the absence of any simple and obvious means of identifying and preselecting only reliable laboratories as participants in certification studies, an investigation was undertaken of the validity of adopting the consensus mean (after outlier elimination) from an interlaboratory study as a certified value. 

Validity of the interlaboratory consensus mean as a certified value... 

Additional evidence of the benefits obtained when the traceability of interlaboratory data to a common, reliable measurement standard is established is shown in Table 3. The interlaboratory consensus mean obtained when all laboratory data are traceable to the common standard is in very good agreement with the value obtained by the application of definitive IDMS methodology. 

Some words and phrases don t need a modifier, because the specific is implied in the general. For instance, the word consensus means general agreement. Therefore, modifying it with the word general is repetitive. Similarly, mathematics is a field of study, so it does not need to be modified with the words field of. Review these lists of repetitive phrases and be ready to spot them more easily in SAT prompts and answer choices. 

Table I lists the catalyst materials characterized and available for use as reference materials. For each property measured, the number of the ASTM Standard Test Method used in the determination is identified the material is specified the consensus mean value determined is listed the interlaboratory reproducibility and the intralaboratory repeatability from round robin tests are presented and the number of the ASTM research report describing the round robin data is listed. These round robins were conducted in accordance with ASTM E-691 -- Standard Practice for Conducting an Interlaboratorv Study to Determine the Precision of a Test Method.

Property Test Method Test Material Consensus Mean Reoroducibilitv Repeatability Report... 

The test requires the use of a standard batch of gas oil as a feedstock and a set of equilibrium fluid cracking catalysts with consensus mean conversion values assigned in a reactor of specified design. The gas oil and the set of equilibrium cracking catalysts are useful reference materials. Conversion for any equilibrium or laboratory-deactivated fluid cracking catalyst can be measured and compared to a conversion calibration curve. Conversion is measured by the difference between the amount of feed used and the amount of unconverted material. The unconverted material is defined as all liquid product with a boiling point above 216°C. 

The reports provided to participants in external quality assessment schemes should contain a munb of important values. As illustrated in Fig. 5, most schemes include data such as the number of participants accepted in the final analysis, the mmiber rejected, i.e. the outliers, the mean and standard deviation of the accepted results, the spiked value together with the individual participant s value and its standard deviation interval (si) from the consensus mean. In addition, a computerised frequency distribution histogram is generally provided. 

In an attempt to categorise individual laboratory performance, several schemes have introduced a performance index. The calculation of the performance index varies from one scheme to another. The original BARTSCONTROL performance index was based upon ranking the difference between reported and consensus mean values (without sign). These index values ranged from 1 to 10 with 1 indicating a good performance... 

The group consensus of opinion was that the pizza crust tasted like cardboard. [ Consensus means collective opinion, so it s unnecessary to add group or repeat opinion. ]... 

Table 3 Comparison of bias percentages from reference method values (RMV) and consensus mean values (CMVs) within two national short-term (ST) surveys...

Taking into account also the preanaiytical variation associated with sampling and sample pre-treatment, the total standard uncertainty with traceability stated to the consensus mean is given by ... 

In case several laboratories use the same analytical reagent systems, a subgrouping of consensus means is often performed. When considering uncertainty, it should then be distinguished between traceability to the subgroup consensus and the overall consensus mean. 

Control limit for accuracy = Consensus mean 1.96 x o-reproducibiiity... 

One of the major disadvantages of using a consensus mean value instead of the true value is that it can never be stated with absolute certainty whether a result which appears to be outside the range of acceptability is in fact closer to the true value than the consensus mean. However unlikely, it may be that a majority of laboratories have generated poor results and a small number of laboratories have generated good results but it is the minority of laboratories that are assessed as poor performers. This situation could be avoided if certified reference materials were distributed. However, there are few reference materials that closely match or resemble all relevant matrices and determinands of interest, including concentration levels. 

Figure 3 (A) Ordered results from a proficiency test of 12 analysts. The amount of substance concentration of carbonate in the distributed test solution was assigned as 27.8+0.2 mmol I with a target standard deviation for the group of I.OmmolP The consensus mean was 28.9mmoll with a sample standard deviation of 1.3 mmol I No points were outliers by a Grubbs test. (B) Data of (A) transformed to a z-score. Filled circles z, = ((x,- - Assigned value)/Target standard deviation), Open squares z,-= ((z -- Consensus mean)/Sample standard deviation). Lines are drawn at z= +2 and +3.

Statistical Analysis of Results and Performance Characteristics. A common problem with most external quality assurance systems has been the determination of the true value for a control sample. Because the true value is an ideal concept, the data are evaluated against the estimated true value, which may be established from (1) the amount of analyte spiked to the test samples (2) a group of reference laboratories using definitive or reference methods (3) the consensus mean, which is the mean of the results obtained by the participants after exclusion of outlier. It is the responsibility of the coordinators to ensure and demonstrate that the reference values are reliable [6]. 

After exclusion of outlier according to Dixon, Grubb, and Cochran as presented in Ref. 5, the parameters (mean, standard deviation, etc.) are calculated. One-way analysis of variance and outlier tests are applied to estimate the components of variance, repeatability, and reproducibility parameters. In the evaluation report often several performance parameters are given, i.e., the arithmetic mean, geometric mean, consensus mean, mean of results from different groups of analyses, and so forth, and a histogram of all results at the very least. For the validation of each laboratory a performance score is calculated. 

The CTQ program pools analytical results from many participating laboratories to derive consensus mean values for each of the samples distributed. Results reported by each laboratory then are compared against these consensus means for the analyzed samples to determine the relative performance of each laboratory. The proficiency of a participating laboratory is a function of the extent of agreement between results submitted by the participating laboratory and the consensus values for the set of samples analyzed. 

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