Estimation of Uncertainty in Quality Control Tests & Results...........

Calculating Uncertainty of Measurement

Some Important Terms

1.         Uncertainty

                                 Uncertainty is deviation from the true value and can only be expressed in the form of a range, e.g. +3, +10.6, +0.07, etc.

Published Definition:

Uncertainty is a quantification of the doubt about the measurement result.

2.         Error Vs Uncertainty

Error expresses a problem and can only be expressed (in statistical terms) as either positive or negative value, while uncertainty cannot be expressed in the form of a single value.

Published Definition of Error:

Error is the difference between the measured value and the ‘true value’ of the thing being measured.

3.         Sources of Uncertainty

a.         Test / Calibration Performer(s)

It is the uncertainty of the person performing the test / calibration, but as a person’s error cannot be calculated in the form of numerical values that be used in advanced combined estimations, we determine Repeatability and Reproducibility through the test/ calibration results they achieve.

Uncertainty of Repeatability:

It is the deviation found in results when an activity is repeatedly performed under the same condition and by the same person.

Uncertainty of Reproducibility:

It is the deviation found in results when an activity is repeatedly performed on the same type of sample under different conditions (in our case we suggest changing the performer only and try to sustain the rest of the uncertainty sources’ condition as much as possible).

b.         Method used

It is uncertainty expressed in the test / calibration method (equipment manual, etc.) when some assumptions have to be made due to limitation of features and/or resources.

c.         Accessories

The apparatus and accessories being used have uncertainty of their own. In most cases it can be found in their manuals, on their label or their certificates. Experienced personnel who are capable of performing test / calibration of equipment are also able to find its uncertainty, if it’s not given in any other source.

d.         Material, Sample and Chemical

Any material and/or sample being used has its own uncertainty, which is usually provided with its certificate, literature or container. If it’s not provided, personnel can calculate it by comparing it with a reference standard where uncertainty is already stated.

4.         Types of Uncertainty

a.         Type A

Value of Uncertainty achieved through statistical calculation. We use Type A for calculation of two sources of uncertainty which are Repeatability and Reproducibility.

b.         Type B

Value of Uncertainty achieved from any other source e.g. manuals, certificates, etc.

If you are interested in calculation of  Type A or B, you can further comment or just drop me a mail  on qc.macandrains@gmail.com. I'll provide you with formulas and methods used to calculate these types.

Regards 

Khawaja Asad Aslam

Introduction to ISO 17025 (Lab Management System)

Introduction

The first edition (1999) of this International Standard was produced as the result of extensive experience in the implementation of ISO/IEC Guide 25 and EN 45001, both of which it replaced. It contained all of the requirements that testing and calibration laboratories have to meet if they wish to demonstrate that they operate a management system, are technically competent, and are able to generate technically valid results.

The first edition referred to ISO 9001:1994 and ISO 9002:1994. These standards have been superseded by ISO 9001:2000, which made an alignment of ISO/IEC 17025 necessary. In this second edition, clauses have been amended or added only when considered necessary in the light of ISO 9001:2000.

Accreditation bodies that recognize the competence of testing and calibration laboratories should use this International Standard as the basis for their accreditation. Clause 4 specifies the requirements for sound management. Clause 5 specifies the requirements for technical competence for the type of tests and/or calibrations the laboratory undertakes.

Growth in the use of management systems generally has increased the need to ensure that laboratories which form part of larger organizations or offer other services can operate to a quality management system that is seen as compliant with ISO 9001 as well as with this International Standard. Care has been taken, therefore, to incorporate all those requirements of ISO 9001 that are relevant to the scope of testing and calibration services that are covered by the laboratory's management system.

Testing and calibration laboratories that comply with this International Standard will therefore also operate in accordance with ISO 9001.

Conformity of the quality management system within which the laboratory operates to the requirements of ISO 9001 does not of itself demonstrate the competence of the laboratory to produce technically valid data and results. Nor does demonstrated conformity to this International Standard imply conformity of the quality management system within which the laboratory operates to all the requirements of ISO 9001.

The acceptance of testing and calibration results between countries should be facilitated if laboratories comply with this International Standard and if they obtain accreditation from bodies which have entered into mutual recognition agreements with equivalent bodies in other countries using this International Standard.

The use of this International Standard will facilitate cooperation between laboratories and other bodies, and assist in the exchange of information and experience, and in the harmonization of standards and procedures

www.ISO.org

Ref: 

Good Laboratory Practice

In the clinical and research arena, the phrase good laboratory practice or GLP generally refers to a system of management controls for laboratories and research organizations to ensure the consistency and reliability of results - as outlined in the Organisation for Economic Co-operation and Development (OECD) Principles of GLP and national regulations.
GLP was instituted following cases of safety and efficacy test fraud by pharmaceutical & industrial manufacturers; as a standard meant to ensure the quality, integrity, and reliability of safety data.

GLP applies to non-human (clinical) studies conducted for the assessment of the safety of chemicals to man, animals and the environment.
The internationally accepted definition reads:Good Laboratory Practice (GLP) embodies a set of principles that provides a framework within which laboratory studies are planned, performed, monitored, recorded, reported and archived. These studies are undertaken to generate data by which the hazards and risks to users, consumers and third parties, including the environment, can be assessed for pharmaceuticals (only preclinical studies), agrochemicals, cosmetics, food additives, feed additives and contaminants, novel foods, biocides, detergents etc.... GLP helps assure regulatory authorities that the data submitted are a true reflection of the results obtained during the study and can therefore be relied upon when making risk/safety assessments.
GLP can become confused with the standards of laboratory safety - wearing appropriate gloves, glasses and clothing to handle materials safely.