One of the best ways for a laboratory is to monitor its performance it to participate in proficiency testing scheme. Proficiency testing is a type of inter-laboratory comparison exercise in which samples are circulated to the participating laboratories, results are then collated and evaluated centrally. Each laboratory is then informed of its performance relative to the other laboratories in the scheme and relative to either true or consensus result for the sample. Performance is usually quoted in terms of the number of standard deviations between the achieved value and the consensus or true value. In some schemes participants are given a pass /fail rating.

Because of the requirement of the laboratory accreditation bodies from all over the world more and more laboratories participate in proficiency testing schemes. Since in all fields of testing and calibration, the satisfactory performance by an applicant laboratory is the pre-requisite from the accreditation bodies, participation in PT is increasingly being used by laboratories. Moreover PT is being increasingly used by laboratories to demonstrate their competence and thus it is becoming more popular and acceptable to laboratories. Laboratories do face a problem as there are not adequate numbers of PT schemes to meet their need. While many laboratory accreditation bodies organize their own PT schemes many accreditation bodies do use PT schemes or other inter-laboratory comparison schemes being operated by others to evaluate the competence of their accredited laboratories.

To cope up with the increasing requirement for PT schemes or inter-laboratory comparison many commercial third party PT and inter-laboratory comparison providers are entering the market to fill the gap and thus meet the growing need. This has led to the need for maintaining a common standard for operating the inter-laboratory comparison programs. This need is met by operating the inter-laboratory comparison schemes as per the guidance given in ISO/IEC Guide 43 part I. which is currently being revised as a standard, ISO 17043.

Some accreditation bodies have started giving accreditation to PT/ Inter-laboratory comparison program providers based on Guide 43.

2.Overall suitability of the design of specific proficiency testing program

4.1.1 ISO/IEC Guide 43 Part-1 and ISO/IEC Guide 43 Part-2, deal with all those issues which are technical & relating to the conduct of PT programs, such as "Development and operation of proficiency testing schemes" and "Selection and use of proficiency testing schemes by laboratory accreditation bodies" respectively.

4.1.2 APLAC MR 001 "Procedures for establishing and maintaining mutual recognition arrangements (MRA) amongst accreditation bodies" Includes the requirements which accreditation bodies are expected to apply when approving laboratory's arrangements for proficiency testing.

• One PT activity prior to gaining accreditation

• One PT activity relating to each other major sub-area of major disciplines of a laboratory's scope of accreditation at least every four years

ILAC-G13;2000 "Guidelines for the requirements for the competence of providers of PT schemes" This document spells its need for PT program.

- Test methods and methods validation ( Clause 5.4 of ISO/IEC 17025) Validation of methods (clause 5.4.5.1 Note 2)

- Measurement traceability ( Clause 5.6.2..2 of ISO/IEC 17025) Participation in a suitable program of inter-laboratory comparison, where required.

- Assuring the quality of test and calibration results, ( Clause 5.9.1 b of ISO/IEC 17025))

Clause 7.12.1 (ISO/IEC 17011) The accreditation body shall have and apply procedures to demonstrate the competence of its accredited laboratories by their satisfactory participation in proficiency testing activity, where such activities are available and appropriate. Where such activities are available and appropriate, the minimum amount of proficiency testing shall be specified. The amount of proficiency testing and frequency of participation have to be seen in relation to other surveillance activities.

Clause 7.12.2 (ISO/IEC 17011) The accreditation body may organize proficiency testing or other inter-laboratory comparisons itself or may involve another body, judged to be competent.

Clause 7.12.3 (ISO/IEC 17011) The accreditation body shall ensure that proficiency testing activities that its accredited or applicant laboratories have to undertake are effective, linked to the assessment process and appropriate corrective action are carried out when necessary.

Clause 7.12.4 (ISO/IEC 17011) The accreditation body shall take into consideration, where relevant, the performance of laboratories in proficiency testing, when evaluating the competence of the staff and the validity of the results.

Clause 7.12.5 (ISO/IEC 17011) The accreditation body shall maintain a list of proficiency testing programs.

The agency which need to conduct PT programs is required to meet the obligation that may applicable to it. ISO/IEC Guide 43 I & II give the details for methodology to be followed in organizing a PT scheme.

3. Roles & uses of Proficiency Testing Programs

• Determines the performance of the individual laboratory & monitors laboratory's performance

• Identify problems in the laboratory and initiate remedial action

• Establish effectiveness & comparability of non standard test and calibration methods, i.e. validation of a test method

• Identify inter-laboratory differences

• Assign values to the reference materials (RMs) and assess their suitability for use in specific test and measurement procedures

• Establish traceability in measurements where calibrations are not possible or available and/or RMs/ CRMs are not available

• Participants of a PT scheme normally use the method of test or calibration of their choice, which in consistence with the routine procedure being used by them. However in those cases where they have developed a test method or they intend to use a non-standard method they use a PT Program to validate.

• In certain cases, a coordinator may ask the participants to use specified method. Such methods are usually internationally accepted standard methods.

• Where a calibration procedure is used, the assigned value will often be a reference value obtained from a high -echelon calibration laboratory, National Standards Laboratory , and should use well defined accepted procedures.

• Where participants are free to use a method of their choice, the coordinator may ask for details of method used to allow the use of participants results to compare and comment on the methods.

5.Types of PT scheme

Proficiency testing techniques vary depending on the nature of the test item, or material test method in use and the number of laboratories participating, or as per the requirement of client of lab and the regulatory authorities. The common feature in most of the PT programs is the comparison of test results obtained from participating laboratories using statistical methods. In some programs, one of the participating laboratories may be controlling and, coordinating. The most commonly used types of PT schemes are:

Measurement comparison schemes involve circulation of the calibrated item/ artifact from one participating laboratory to the other, for the relevant measurement.

The reference value of the artefact is from a National Metrology Laboratory/Reference Laboratory, which is also in most of the cases is the coordinating laboratory and assigns values to the test item/artefact. This type of program may take a considerable time to complete the cycle of measurement. As the artefact is under circulation the coordinating laboratory ensures the integrity of the artefact.

Such an activity takes care of the range off measurement and also the uncertainty in measurements.

The individual measurement results are compared with the reference value established by the National Metrology Laboratory/Reference Laboratory. The coordinator is required to take into account the claimed measurement uncertainty of each participating laboratory. Items used (artefacts) in this type of proficiency testing are reference standards ( resistors, gauges and instruments.). The path travelled by artifact is depicted below:

• Inter-laboratory testing schemes involve randomly selected sub-samples, demonstrated to be homogeneous, being distributed simultaneously to participating testing laboratories for concurrent testing. After completion of the testing, the results are returned to the coordinating body, and compared with the assigned value(s), to give an indication of the performance of the individual laboratories. The important features are:

• Sub samples given to each laboratory are homogenous.

• After completion of testing, results are returned to the coordinating laboratory and compare with an assigned values to give an indication of performance of the individual laboratory.

• Items used in this type of PT are food, body fluids, water, soil and other environmental materials. Refer ISO/IEC Guide 43-1:1997.

6.Steps involved in organizing a PT program

• Announcement of PT activity & inviting interest in PT participation from labs
• Sending of samples to participating laboratory or ensuring for circulation of artefact amongst the participant labs
• Receive the results from lab
• Do the statistical analysis and send preliminary report to participating laboratories
• Incorporation of feedback from laboratories
• Sending final report to participating labs after receiving corrective action

7.Responsibilities & Authorities of the PT Program coordinator

PT Program coordinator shall have a PT committee with an expert on statistics and on the subject as its member besides other members with appropriate knowledge on the testing/calibration of the substance / item. In addition the body, shall:

• Define responsibilities and functioning of PT Committee as the coordinator.
• To oversee, the development of PT programs covering calibration and testing laboratories.
• To oversee all work and activities in relation to the conduct of PT programs.
• To create a web-site, to disseminate the information about PT Schedules.
• To facilitate interested laboratories, so as to participate in forthcoming programs if interested.
• Maintains the records of the completed PT programs
• Comply with the requirements given in- ISO/IEC Guide 43, volume I and II, to manage the PT activity.

• ISO/IEC Guide 43Part-1 "Development and operation of proficiency testing scheme"
• ISO/IEC Guide 43 Part-2 "Selection and use of proficiency testing scheme by laboratory accreditation bodies"

8.Organization and design of PT scheme

• the name and address of the organization conducting PT program.
• the name and address of the coordinator
• nature and purpose of program/ nature of the test item/ test to be performed
• procedure for selection of participants
• the expected initial and target dates /deadlines of PT Scheme. Date for submission of results of testing.

9.Selection and preparation of appropriate test samples or measurement artefacts (Test item preparation)

• test item/material to be distributed should be similar in type to those routinely tested.
• the assigned value should not be disclosed to the participants until after the result have been collated.
• procedures for sampling, randomizing, transporting, sorting and handling of the test items or materials to be documented.
• bulk material prepared for PT must be sufficiently homogenous for each test parameter to ensure laboratories receive similar material.

10.Sample stability and transportability considerations

• PT provider shall use a statistically random selection of a representative number of samples from a batch of test material to assess the homogeneity of the material. And the PT provider shall have a documented assessment procedure. Assessment shall be conducted in accordance to statistical design. In case of measurement artefacts, preliminary stability checks shall be made and periodic checks of assigned property values is carried out through out the course of the scheme.

• it should be ensured and demonstrated that test items are sufficiently stable and have not undergone any significant change throughout the conduct of proficiency test.

• PT provider shall provide proper packaging to the extent necessary to ensure conformity with relevant regional, national or international safety and transport requirements.

• The PT provider shall ensure that material labels are securely attached to the product packaging of individual units and are designed to remain legible and intact within the period of use in a proficiency test.

11.Testing/calibration/ data analysis

• The coordinator shall ensure that the participating laboratories have used the standard process of testing/calibration for which the program has been designed.

• the data received from laboratories must be entered and analyzed and reported back to participants.

12.Statistical methods for treatment of PT data

The statistical technique used to analyze, the results need to be appropriate for each situation. These are three steps:

• determination of assigned value
• calculation of performance statistics
• evaluation of performance

12.1 Determination of assigned values and its uncertainty

There are many methods for the establishment of assigned values. The most common procedures are listed below:

c.. Reference values- as determined by analysis, measurement or comparison of the test item alongside a reference material or standard, traceable to national or international standard.

d.. Consensus value from expert laboratories - expert laboratories should have demonstrable competence in the determination of the measurand (s) under test, using validated methods known to be highly precise and accurate, and comparable to methods in general use.

12.3The following statistics are used when assigned values are determined by consensus technique:

a. Qualitative value - consensus of a predetermined majority percentage ( usually expressed ona nominal or ordinal scale)

b Quantitative value - "average" for an appropriate comparison group such as:

• mean, which may be weighted or transformed ( e.g. geometric mean,robust mean)

• median, mode or other robust measure.

Where appropriate, the uncertainty of the assigned values should be determined using procedures described in Guide to the expression of uncertainty in measurement.

When participants results are used to determine the assigned values, it is done by using robust statistical methods or by removing outliers prior to calculations (ISO 5725- 2 ). In larger schemes, it may be possible to have automated outliers screens.

a If results are removed as outliers, they are removed only for calculation of summary statistics. These results are still to be evaluated with in the proficiency scheme and given an an apropriate performance rating.

NOTE: 1. When assigned values are determined by reference or participant consensus, the coordinator should have a procedure to establish the trueness of the assigned values and for reviewing the distribution of the data.

NOTE: 2. The coordinator should have the criteria for the acceptability of an assigned value in terms of its uncertainty.

NOTE: 3. Organizing a PT or the inter-laboratory comparison program always needs involvement of more than ten laboratories to facilitate performing statistical analysis of the data obtained from laboratories.

13.Calculation and evaluation of performance

The objective is to measure the deviation from the assigned value to compare with performance criteria. And it needs transforming proficiency test results to be into a performance statistic, so to be able to do comparison with defined goals. Variability measures are often used for calibration of performance statistics. Common examples of such variability measures for an appropriate comparison include:

• Standard deviation 's' (SD)
• Coefficient of variation (CV) or relative standard deviation (RSD)
• Percentile, median absolute deviation or other robust measures

• Difference (x - X), where "x" is participating result and X is the assigned value
• Percentage(%) difference (x - X) x 100 / X
• Percentile or rank

' s ' an appropriate estimate/measure of variability which is selected to meet the requirements of the scheme. (e.g. standard deviation). This model can be used both in the situation where X and s are derived from participants results or when X and s are not derived the participants results. [ for example when assigned values and variability are specified.

and Ukb is the uncertainty of a participants result and Uref is the uncertainty of the reference laboratory's assigned value. For En numbers, evaluating performance

Assigned values should be determined to evaluate participants fairly. This is accomplished through selection on common comparison groups, wherever possible, and the use of common assigned values.