ISO 13528

STATISTICAL METHODS USED IN ISO 13528 INTERLABORATORY COMPARISON AND PROFICIENCY TESTING

ISO 13528:2022 The standard is an international standard that covers statistical methods used in proficiency tests made through interlaboratory comparison. This standard provides detailed information on designing proficiency tests, analyzing the data obtained and interpreting the results.

Purpose of the Standard

• Increasing the reliability of proficiency tests: The standard aims to increase the reliability of the results by ensuring that proficiency tests are conducted on a scientifically and statistically sound basis.
• Evaluating the performance of laboratories: It provides an objective framework for assessing how competent laboratories are with certain testing methods or measurement processes.
• Guiding accreditation bodies: It guides accreditation bodies regarding evaluation criteria and acceptability limits during the accreditation process of proficiency tests.

Scope of the Standard

• Design of proficiency tests: It covers topics such as statistical methods and sample size calculations for the design of different types of proficiency tests (open, blind, double-blind, etc.).
• Data analysis: It provides guidance on appropriate methods for statistical analysis of the data obtained (e.g. analysis of variance, regression analysis) and interpretation of the results.
• Evaluation of the results: It provides information about the statistical measures (e.g., z-score, Cohen's kappa) and acceptability limits used to evaluate the performance of participating laboratories.

Importance of the Standard

• Quality assurance: The reliability of measurement results affecting the quality of products and services can be verified by proficiency tests conducted in accordance with the ISO 13528 standard.
• International acceptance: This standard is an accepted and widely used reference point in many countries.
• Continuous improvement: It helps laboratories continuously improve their performance.

For Whom Is It Important?

• Laboratories: This standard is of great importance especially for laboratories that want to be accredited or want to maintain their current accreditation.
• Proficiency testing providers: Organizations that organize proficiency tests must design and evaluate their tests in accordance with this standard.
• Accreditation bodies: During the accreditation process of laboratories, they make evaluations based on the ISO 13528 standard.
• Customers: This standard is also an important indicator for customers who want to be informed about the competence of the laboratories from which they purchase products or services.

The ISO 13528:2022 standard is an important document that covers statistical methods used to reliably evaluate the performance of laboratories. This standard provides many benefits for both the laboratories themselves and their customers.

Purposes of proficiency testing

Proficiency testing (PT) within the ISO 17043 Standard involves the use of interlaboratory comparisons to determine the performance of participants (who may be laboratories, accreditation bodies, or individuals) for specific tests or measurements and to monitor their ongoing performance. Most importantly, they include evaluating laboratory performance, identifying problems in laboratories, determining the effectiveness and comparability of test or measurement methods, providing additional confidence to laboratory customers, verifying claims of uncertainty, and training participating laboratories. The statistical design and analytical techniques applied must be appropriate for the stated purpose(s).

Justification for scoring in proficiency testing schemes

Various scoring strategies are available and used for proficiency testing. Although detailed calculations vary, most proficiency testing schemes compare the participant's deviation from an assigned value to a numerical criterion used to decide whether the deviation is of concern. Therefore, the strategies used to select a criterion for assigning values ​​and assessing participant biases are critical. In particular, it is important to consider whether the assigned value and the criterion for evaluating deviations should be independent of the participant results or derived from the presented results. ISO 13528 standard, both strategies are provided. However, attention is drawn to the discussion to be found in ISO 13528 standard Clauses 7 and 8 on the advantages and disadvantages of choosing criteria for evaluating assigned values ​​or deviations that are not derived from participant results. In general, choosing assigned values ​​and evaluation criteria independently of participant outcomes will appear to provide advantages.

This applies in particular to measures used to evaluate deviations from the established value, such as the standard deviation for adequacy assessment or a margin for measurement error; In such measures, a consistent selection based on the suitability of the measurement results for a particular end use is particularly useful.

ISO 13528 and ISO/IEC 17043

This document provides support for the implementation of ISO/IEC 17043, in particular the requirements for statistical design, validation of proficiency test items, review of results and reporting of summary statistics. The statistical techniques used for a particular proficiency testing scheme are expected to evolve as the scheme matures; Scores, evaluation criteria and graphical techniques will be developed to better meet the specific needs of the target participant group, accreditation bodies and regulatory authorities.

ISO 13528 includes the published guidance for proficiency testing of chemical analytical laboratories, but additionally includes a broader range of procedures that allow their use in conjunction with valid measurement methods and qualitative descriptions.

ISO 13528 includes statistical techniques consistent with other International Standards, in particular TC69/SC6, in particular Accuracy: the ISO 5725 series of standards on accuracy and precision. The techniques also aim to reflect other International Standards where appropriate and are intended to be consistent with ISO/IEC Guide 98-3 (GUM) and ISO/IEC Guide 99 (VIM).

Statistical expertise

ISO/IEC 17043 stipulates that to be competent, a proficiency testing provider must have access to statistical expertise and authorize certain personnel to perform statistical analysis. Neither ISO/IEC 17043 nor ISO 13528 can further specify what this required expertise is. For some applications an advanced degree in statistics is useful, but often specialization needs can be met by individuals with technical expertise in other areas who are familiar with basic statistical concepts and have experience or training in common techniques applicable to the analysis of data from proficiency testing schemes. If a person is responsible for statistical design and/or analysis, it is critical that that person have experience with interlaboratory comparisons, even if that person has an advanced degree in statistics. Traditional advanced statistics training does not generally include exercises involving interlaboratory comparisons, and the unique causes of measurement error in proficiency testing may appear unclear. The guidance in this document cannot provide all the expertise needed to evaluate all applications and is not a substitute for experience gained in working with interlaboratory comparisons.

computer software

Computer software required for statistical analysis of proficiency testing data can vary widely, from simple spreadsheet arithmetic for small proficiency testing schemes using known reference values ​​to complex statistical software used for statistical methods based on iterative calculations or other advanced numerical methods. Many of the techniques in this document can be performed with traditional spreadsheet applications, perhaps with routines customized for a particular proficiency testing scheme or analysis; Some techniques will require freely accessible computer applications. In all cases, users are expected to verify the validity and accuracy of their calculations, especially when specific routines are entered by the user. However, even if ISO 13528 standard techniques are appropriately and accurately implemented by appropriate computer applications, they cannot be applied without the attention of an individual with sufficient technical and statistical expertise to understand the nature of the applications and statistical assumptions and to identify and investigate anomalies that may occur in any round of a proficiency testing scheme.

Scope

ISO 13528 provides detailed descriptions of statistical methods that proficiency testing providers can use to design proficiency testing schemes and analyze data from those schemes. ISO 13528 provides recommendations on the interpretation of proficiency testing data by participants in such proficiency testing schemes and by accreditation bodies.

The procedures included in ISO 13528 can be applied to demonstrate that measurement results obtained by laboratories, inspection bodies and individuals meet the specified criteria for acceptable performance.

ISO 13528 can be applied to proficiency testing where the results are quantitative measurements or qualitative observations of test items.

ISO 13528 Standard Content

4 General principles

4.1 General requirements for statistical methods

4.2 Basic model

4.3 General approaches to evaluating performance

5 Guidelines for the statistical design of proficiency testing programs

5.1 Introduction to statistical design of proficiency testing programs

5.2 Basis for a statistical design

5.3 Considerations for statistical distribution of results

5.4 Considerations for small numbers of participants

5.5 Guidelines for selecting reporting format

5.5.1 General requirements for reporting format

5.5.2 Reporting of duplicate measurements

1. Reporting 'less than' or 'greater than' a limit (censored data)

5.5.4 Number of significant digits

6 Guidance for initial review of proficiency test samples and results

6.1 Homogeneity and stability of proficiency test samples

6.2 Considerations for different measurement methods

6.3 Error removal

6.4 Visual review of data

6.5 Robust statistical methods

6.6 Outlier techniques for individual results

7 Determination of assigned value and standard uncertainty

7.1 Selection of the method for determining the assigned value

7.2 Determining the uncertainty of the assigned value

7.3 Formulation

7.4 Certified reference material

7.5 Results obtained from a laboratory

7.6 Consensus value obtained from expert laboratories

7.7 Consensus value from participant results

7.8 Comparison of the assigned value with an independent reference value

8 Determination of criteria for evaluating performance

8.1 Approaches to determining evaluation criteria

8.2 According to experts' perception

8.3 Based on experience from previous rounds of a proficiency testing program

8.4 Using a general model

8.5 Using repeatability and repeatability standard deviations from a previous collaborative study on the precision of a measurement method

8.6 From data obtained in the same round of a proficiency testing programme.

8.7 Monitoring interlaboratory agreement

9 Calculation of performance statistics

9.1 General considerations for determining performance

9.2 Limiting the uncertainty of the assigned value

1. Bias estimates (measurement error)

9.4 Z scores

9.5 z' scores

1. Zeta scores (ζ)

At 9.7 Points

9.8 Evaluation of participant uncertainties in testing

9.9 Combined performance scores

10 Graphical methods for defining performance scores

10.1 Application of graphical methods

10.2 Histograms of results or performance scores

10.3 Kernel density graphs

10.4 Bar charts of standardized performance scores

10.5 Youden plot

10.6 Graphs of repeatability standard deviations

10.7 Split examples

10.8 Graphical methods for combining performance scores across several rounds of a proficiency testing program

11 Design and analysis of qualitative proficiency testing programs (including nominal)

1. row properties)

11.1 Qualitative data types

11.2 Statistical design

11.3 Values ​​assigned for qualitative proficiency testing programs

11.4 Performance evaluation and scoring for qualitative proficiency testing programs

Annex A (normative) Symbols

Annex B (informative) Homogeneity and stability of proficiency test samples

Appendix C (informative) Solid analysis

Appendix D (informative) Additional guidance on statistical procedures

Appendix E (informative) Illustrative examples

Appendix F (Informational) Example of computer code for plotting and resampling analysis (“bootstrap”) of PT results

Comprehensive Information About ISO 13528:2022 Standard Training

ISO 13528:2022 Standard It is an important international standard that comprehensively addresses statistical methods used in interlaboratory comparison experiments. This standard aims to establish a scientific basis for the methods used to evaluate the competence of laboratories and ensure the reliability of the results.

Purpose of Education

ISO 13528:2022 standard training aims to provide participants with knowledge and skills on the following subjects:

• Purpose and importance of proficiency tests: To understand why interlaboratory comparison experiments are performed, how these experiments affect the quality of laboratories and their role in accreditation processes.
• Basic concepts of statistical methods: To learn the basic principles of statistical methods such as data analysis, variance analysis, regression analysis.
• Requirements of the ISO 13528:2022 standard: To examine the content of the standard in detail and to learn which statistical methods should be used in interlaboratory comparison experiments.
• Data analysis software: To gain practical knowledge on the use of statistical analysis software such as SPSS and Minitab.
• Reporting: To gain the necessary skills to report the results obtained accurately and clearly.

Who is the training aimed at?

• Laboratory managers: Managers who want to evaluate and improve the competence of their laboratories.
• Quality assurance experts: Experts who want to increase the effectiveness of quality systems and ensure that laboratories comply with international standards.
• Laboratory technicians: Technicians who want to ensure the accuracy and reliability of test results.
• Employees of accreditation bodies: Personnel who make evaluations in the accreditation processes of laboratories.
• Statisticians: Statisticians who work in this field and want to improve their knowledge.

Training Content (Generally)

• Entrance: The importance of interlaboratory comparison experiments and the purpose of the ISO 13528 standard
• Basic concepts of statistical methods: Data distributions, measures of central tendency, measures of variability
• Design of proficiency tests: Sample selection, experimental protocols, data collection
• Data analysis: Data cleaning, visualization, statistical tests
• Evaluation of the results: Performance evaluation criteria, reporting
• Software applications: Practical applications with statistical analysis software

What Do You Gain at the End of Training?

• Comprehensive information about the ISO 13528:2022 standard
• Ability to design and analyze interlaboratory comparison experiments
• Ability to use data analysis software effectively
• Increasing the reliability of test results
• Becoming more successful in international accreditation processes

Participant Profile: Organizers and laboratories who want to be accredited according to the ISO 17043 Standard, laboratory managers who want to have the qualifications to implement, develop and manage these systems, and human resources and laboratory personnel who want to have a career in laboratory standards can participate in these trainings.

Exam: Exam can be taken at the end of the training.

Trainer: Provided by our International Chief Auditor and Training Experts. Announced Before Training.

Training Date: Announced Before Training.
Training Duration: 3 days.
Training Location: Online/In-house.
Certificate: At the end of the training, a certificate is given to those who attended the training.