Proficiency score

What are your individual proficiency scores and their classification, (e.g. z-scores or equivalent), over the past two years, for the analyte/matrices of relevance to this proposal ... 

Proficiency testing can be assessed in different ways. One of the most used evaluation system is that of so-called z-scores which are defined as follows (Lawn et al. [1993] Thompson and Wood [1993]) ... 

There are a number of different performance scoring systems used in proficiency testing schemes. The most commonly used system is the z-score, which... 

En numbers are used when the assigned value has been produced by a reference laboratory, which has provided an estimate of the expanded uncertainty. This scoring method also requires a valid estimate of the expanded uncertainty for each participant s result. A score of En < 1 is considered satisfactory. The acceptability criterion is different from that used for z-, z - or zeta-scores as En numbers are calculated using expanded uncertainties. However, the En number is equal to zeta/2 if a coverage factor of 2 is used to calculate the expanded uncertainties (see Chapter 6, Section 6.3.6). En numbers are not normally used by proficiency testing scheme providers but are often used in calibration studies. 

In Section 7.3.3, we learned about one of the most common scoring systems used in proficiency testing - the z-score - and how laboratory performance can be judged as being satisfactory, questionable or unsatisfactory. How should a laboratory act on the performance scores it receives Action should be considered in the following situations ... 

Participation in proficiency testing schemes is an ongoing activity. It is therefore useful to monitor performance over a period of time and to look for trends. Performance over time can be demonstrated statistically by using measures such as RSZ and SSZ (see Section 7.3.4) but as mentioned previously, these can be misleading. It is better to monitor performance scores by plotting them on a... 

Most proficiency testing schemes compare bias with a standard error. An obvious approach is to form the z-score given by ... 

As z is standardised, it is comparable for all analytes and methods. Thus values of z can be combined to give a composite score for a laboratory in one round of a proficiency test. The z-scores can therefore be interpreted as follows ... 

There are several methods of combining the z-scores produced by a laboratory in one round of the proficiency test described in the Protocol. They are ... 

All should be used with caution, however. It is the individual z-scores that are the critical consideration when considering the proficiency of a laboratory. 

For proficiency tests z-seores have been widely nsed for mat r years. Z-scores represent the deviation from the assigned valne in standard deviation units. The standard deviation may be calculated after exelusion of outiiers or with robust statistios. In some eases it is set to a eertain value aeeording to the quality targets of the PT provider. 

Two approaches attempt to solve this problem. The one is a transformation of the data to logarithms prior to the statistical calculations corresponding to a logarithmic normal distribution. The other is a modification of the z-scores with correction factors. This method was introduced first in a German standard for proficiency testing (DIN 38402 - 45), which in the meantime partially was transferred into ISO/TS 20612. 

AMC (2000) How to combine proficiency test results with your own uncertainty estimate - the zeta score. AMC Technical Brief No. 2 (Nov 2000). Analytical Methods Committee, Royal Society of Chemistry, London, 2 pp. 

The grading of these tests varies as well. Many departments rank candidates based on their scores in several areas, including the CPAT and the written exam. Others rank you primarily for proficiency on the... 

Participance in Proficiency Testing Schemes Proficiency testing (PT) is the periodic assessment of the competency or the analytical performance of individual participating laboratories [23]. An independent coordinator distributes individual test portions of a typical uniform test material. The participating laboratories analyze the materials by their method of choice and return the results to the coordinator. Test results obtained by different laboratories are subsequently compared with each other and the performance of each participant evaluated based on a single competency score [64,107]. International harmonized protocols exist for the organization of PT schemes [59,60,64,69,79]. 

Participation in proficiency tests is not a prerequisite or an absolute substitute for IQC measures or vice versa. However, participance in proficiency tests is meaningless without a well-developed IQC system. IQC underlies participance in PT schemes, while IQC and participance in PT schemes are both important substitutes of AQA (Figure 6). It is shown that laboratories with the strongest QC procedures score significantly better in PT schemes [8,50]. Participance in PT can to a certain extent improve the laboratory s performance however unsatisfactory performance in schemes (up to 30% of all participants) has been reported. This means that there... 

In a farsighted move in 1989, the European Union laboratory IRMM started a series of interlaboratory comparisons to provide objective evidence for the degree of equivalence and the quality of chemical measurements by comparing a participant s measurement results with external certified reference values (IRMM 2006). At the time most proficiency testing schemes used consensus results for the mean and standard deviation to derive z scores. With the IMEP-1 analysis of lithium in serum, the world was alerted to the problem of lack of accuracy in analytical measurements. The data of the first IMEP-1 trial are replotted in figure 5.6 notice that the apparent outlier was the only laboratory to come close to the assigned value. 

A CBT/CAT is a test administered at a computer. CBT stands for computer-based test and CAT stands for computer-adaptive test. Special software enables the computer to accurately determine your proficiency at a given task within a short time. In brief, every test taker gets a different set of questions. The computer uses your performance on the early questions to give either easier or more difficult subsequent questions. This is the adaptive part. The harder the questions you successfully answer, the higher your score. You will find more information and specific strategies for CBT/CATs on the following pages. 

An essay with a score of 4 reveals a proficient analysis of the issue. The writing sufficiently articulates meaning. The essay at this level includes the following attributes ... 

The essay with a score of 4 critiques and analyzes the argument proficiently, while adequately communicating meaning. 

The final part of the OPCW proficiency-testing scheme involves a process of evaluation, scoring,... 

The sum of all points scored eventually represents a laboratory s performance in a single proficiency test. The maximum achievable points, however, depends on the total number of spiking chemicals used. As this number varies from test to test, the points scored cannot be used to compare performances between laboratories participating in different proficiency tests. This comparison is achieved with the final letter scoring system, and is shown in Table 9. 

The process of evaluation, scoring, and designation of the OPCW proficiency-testing scheme is shown in Figure 22. The process is known to have three weaknesses, the areas of weakness are highlighted in Figure 22 and summarized in the following ... 

The range for scoring varies from A (i.e. maximum score) to F (i.e. failure of the test). This A, B, C... system allows for comparison of performance in a number of different proficiency tests, in a rather simple and unambiguous way. However, in combination with the previously discussed strict penalty system, the simplicity of this letter system is at the expense of its transparency letter scores below the maximum score A do not reflect the type of error(s) made. 

Figure 23. Simplified overview of evaluation and scoring process of the OPCW proficiency-testing scheme...

---