The international standard ISO has been withdrawn and replaced by the standard ISO. In order to avoid confusion regarding. TECHNICAL ISO/TR REPORT First edition Statistical methods in process management — Capability and performance. Buy UNI ISO STATISTICAL METHODS IN PROCESS MANAGEMENT – CAPABILITY AND PERFORMANCE – PART 2: PROCESS CAPABILITY.
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ISO 22514-2:2013: Statistical methods in process management – Capability and performance – Part 2:
Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it isi found, please inform kso Central Secretariat at the address given below. 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 orISO’s member body in the country of the requester.
The 225114 of preparing International Standards is normally carried out through ISOtechnical committees. Each member body interested 2514 a subject for which a technical committee has beenestablished has the right to be represented on that committee.
International organizations, governmental andnon-governmental, in liaison with ISO, also take part in the work. The main task of technical committees is to prepare International Standards. Draft International Standardsadopted by the technical committees are circulated to the member bodies for voting.
A Technical Report is entirelyinformative in nature and does not have to be reviewed until the data it provides are considered to be nolonger valid or useful.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patentrights. ISO shall not be held responsible for identifying any or all such patent rights. ISO consists of the following parts, under the general title Statistical methods in process management— Capability and performance: Process capability estimates and performance measures [Technical Report]In the future, it is planned to revise ISO It was renumbered before publication to include itin the ISO series.
To comply with such a strategy,any organization will need to evaluate the capability and performance of its key processes. The methodsdescribed in this part of ISO are intended to assist any management in this respect.
These evaluationsneed to be constantly reviewed by management so that actions compatible with continuous improvement canbe taken when required. The content of this part of ISO has been subject to large shifts of opinion during recent times and thisreport attempts to reflect the current position.
The most fundamental shift has been to isk separatewhat is named in this document as capability conditions from performance conditions, the primary differencebeing whether statistical stability has been obtained capability or not performance. This naturally leads ontothe two sets of indices that are to be found in their relevant clauses.
It has become necessary to draw a firmdistinction between these since it has been observed in industry that companies have been deceived abouttheir true capability position due to inappropriate indices being calculated and published. The progression of this part of ISO is from the general condition to the specific and isoo approach leadsto general iiso being presented before their more usual but specific manifestations.
There exist numerous references that describe the importance of understanding the processes at work withinany organization, be it a manufacturing process or an information handling process. As organizations competefor sales with each other, it has become increasingly apparent that it is not only the price paid for a product orservice that matters so much, but also what costs will be incurred by the purchaser from using such a productor service.
The objective for any supplier is to continually reduce variability and not to just satisfy 225144.
Continual improvement leads to reductions in the costs of failure and assists in the drive for survival in anincreasingly more competitive world. There will also be savings in appraisal costs for as variation is reducedthe need to inspect product might disappear or the frequency of sampling might be reduced.
Process capability and performance evaluations are necessary to enable organizations to assess thecapability and performance of their suppliers.
Those organizations will find the indices contained within thispart of ISO useful in kso endeavour. Quantifying the variation present within a process enables judgement of its suitability and ability to meet somegiven requirement.
The following paragraphs and clauses provide an outline of the philosophy required to beunderstood to determine the capability or performance of 22541 process. All processes will be subject to certain inherent variability. This part of ISO does not attempt to explainwhat is meant by inherent variation, why it exists, where it comes from nor how it affects a process.
This partof ISO starts from the premise that it exists and is stable. Process owners should endeavour to understand the sources of variation in their processes. Methods such asflowcharting the process and identifying the inputs and outputs from a process assist in identification of thesevariations together with the appropriate use of cause and effect fishbone diagrams.
It is important for the user of this part of ISO to appreciate that variations exist that will be of a short-term nature as well as those that will be of a long-term nature and that capability determinations using only theshort-term variation might be greatly different to those which have used the long-term variability.
When considering short-term variation, a study that uses only the shortest-term variation, sometimes knownas a machine study, might be carried out. The method required to carry out such a study will be outside thescope of this part of ISO ; however, it should be noted that such studies are important and kso. It should be noted that where the capability indices given in this part of ISO are computed, isk onlyform point estimates of their true values.
It is therefore recommended that, wherever possible, the indices’confidence intervals are computed iiso reported. This part of ISO describes methods by which thesecan be computed. Process capability estimates and performance measures1 ScopeThis part of ISO describes process capability and performance measures that are commonly used. NOTE 2 A characteristic can be qualitative or quantitative.
NOTE 3 There are various classes of characteristics, such as the following: NOTE 2 A characteristic assigned to a product, process or system e. Such a pattern provides all of the numerical value information of the characteristic 2. NOTE 2 The distribution of a characteristic 2. Thus, if meaningfulinformation about the distribution of a characteristic 2. NOTE 3 It is important to know the class of distributions 2.
NOTE 1 The class of distributions can often be fully specified through the values of the appropriate parameters. Here the model is a fully specified one. EXAMPLE 2 A model for the diameter of bolts as in Example 1 could be the class of normal distributions without attempting to specify a particular distribution. Here the model is the class of normal distributions. NOTE 3 For a uso distribution 2.
NOTE 4 For a non-normal distribution, the length of the reference interval can be estimated by means of appropriate probability papers e. NOTE 5 A quantile or fractile indicates division of a distribution into equal units or fractions, e. Quantile is defined in ISO NOTE 1 Tables or functions in statistical computer packages of the standard normal distribution are readily availablewhich give the proportion of process output expected beyond a particular value of interest, such as a specification limit 2.
This obviates the need to work out the statisticaldistribution function given in the example. NOTE 2 The function relates to a theoretical distribution. In practice, with empirical distributions, the parameters arereplaced by estimates. NOTE 2 The outcome is a distribution 2. NOTE 3 In certain circumstances, the standard deviation, Sw, that represents only within subgroup variation can be used as an estimator for St: The value of the ethsetimdaetgorreseStoaf nsdtaSbwilictyonovfetrhgee for a process in a state of statistical control.
A comparison of the two gives an indication of process. Hence Sw should be used with extreme caution. Sometimes, too, the estimator St is preferredto Sw because it has more tractable statistical properties e.
NOTE 4 For a normal distribution, process capability can be assessed from the expression: The choice of z depends on the particular parts per million capability standard used. Typically z takes the value of 3, 4 or 5. If the process capability meets the specified requirements, a z value of 3 indicates an expected 2 parts per millionoutside of specification. Similarly, a z of 4 indicates an expected 64 parts per million and a z of 5 an expected 0,6 parts permillion outside of specification.
NOTE 5 For a non-normal distribution, process capability can be assessed using, for example, an appropriateprobability paper or from the parameters of the distribution fitted to the data. The expression for process capability takesthe asymmetric form: This enables a direct comparison to be made between thedimensional performance of a characteristic and its specified requirements in terms of both location and dispersion.
NOTE 7 Capability conditions are very restrictive and include: NOTE 3 For a non-normal distribution 2. NOTE 3 Care should be exercised in using this measure as it may contain a component of variability due to specialcauses the value of which is not predictable.
NOTE 4 For a normal distribution 2. Thesample size can be made up of m subgroups each of size n. NOTE 5 For a normal distribution 2. Typically z takes the value of 3, 4 or5. NOTE 6 For a non-normal distribution, process performance can be assessed using, for example, an appropriateprobability paper or from the isl of the distribution fitted to the data.
The expression for process performancetakes the asymmetric form: This enables a direct comparison to be made between the dimensional performance of a characteristic and its specified requirements in terms of both location and dispersion.
NOTE 2254 Performance conditions are least restrictive, but include: They are unsuitable for count or attribute data and information concerning the expression of measures for such data will be found later in 4. With non-normally distributed process measurements, the median is often a preferred alternative measure.
This is often estimated from the mean range value, Rtaken from a range R chart when the process is stable and in a state of statistical control as indicated in 5.
Methods used to estimate the process standard deviation are given in Annex A. Methods of calculating the standard deviations representing these 2254 are given in Annex A.
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Very often, when data are gathered over a long period of time, the standard deviation is made larger by the effects of fluctuations in the process. It is compatible with the methods used in off-line quality techniques. Isk are made of how many items do or do not possess the quality attribute or how many such events occur in the item, group of items or unit area.