ISO/TR TECHNICAL REPORT 18532 First edition 2009-04-15 Guidance on the application of statistical methods to quality and to industrial standardization Lignes directrices pour I'application des methodes statistiques a la qualité et a la normalisation industrielle Reference number ISO/TR 18532:2009(E) @ ISO 2009 by IHS under lic Not for Resale ISO/TR 18532:2009(E) PDFdisclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The IsO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by IsO member bodies. In COPYRIGHT PROTECTED DOCUMENT ISO2009 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either isO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 : CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail [email protected] Web www.iso.org Published in Switzerland @IsO2009-All rightsreserved T by IHS unde I without license from IHS Not for Resale ISO/TR 18532:2009(E) Contents Page Foreword .ix Introduction 1 Scope. 2 Normative references. 3 Terms and definitions . 4 Illustration of value and role of statistical method through examples 4.1 Statistical method.. 4.2 Example 1: Strength of wire .... 4.2.1 General ......... 4.2.2 Overalltestresultsandlowerspecificationlimit.... 4.2.3 Initial analysis ... 4.2.4 Preliminary investigation....... 4.2.5 General discussion on findings .... 4.2.6 Explanation of statistical terms and tools used in this example. 4.3 Example 2: Mass of fabric ... 4.3.1 4.3.2 Test results and specification limits 4.3.3 Discussion of specific results.... 4.3.4 Discussion on general findings .... 4.4 Example 3: Mass fraction of ash (in %) in a cargo of coal... 4.4.1 General .... 4.4.2 Test results (reference Iso 11648-1: Statistical aspects of sampling from bulk materials). 4.4.3 4.4.4 Benefits of a statistically sound sampling plan .. 14 4.4.5 General conclusions ... 16 5 Introduction to basic statistical tools.. 16 5.1 General 16 5.2 5.3 Presentation of data ..... ..19 5.3.1 Dot or line plot ... 19 5.3.2 19 5.3.3 Stem and leaf plot... 19 5.3.4 Box plot .. 20 5.3.5 Multi-vari chart 22 5.3.6 Position-Dimension (PD) diagram.... 23 5.3.7 Graphical portrayal of frequency distributions. 25 5.3.8 The normal distribution ... 31 5.3.9 The Weibuli distribution.. 35 5.3.10 Graphs .......... 41 5.3.11 Scatter diagram and regression.. 41 5.3.12 Pareto (or Lorenz) diagram... 5.3.13 Cause and effect diagram...... 6 Variation and sampling considerations ........ 45 6.1 Statistical control and process capability 45 6.1.1 Statistical control .... 45 6.1.2 Erratic variation . 47 6.1.3 Systematic variation... 6.1.4 Systematic changes with time . ..48 6.1.5 Statistical indeterminacy .... 49 ili CopyrghtInternational Organizaionsadardizaonghtsreserved Not for Resale ISO/TR 18532:2009(E) 6.1.6 6.1.7 Qualitylevelandprocesscapability. .. 49 6.2 Sampling considerations .. 50 7 Methods of conformity assessment .. 54 7.1 The statistical concept of a population ........ 54 7.2 The basis of securing conformity to specification.... 7.2.1 The two principal methods ..... .55 7.2.2 Considerations of importance to the customer.. 56 7.2.3 Considerations of importance to the s