DS/ISO 3951-4:2011

Sampling procedures for inspection by variables - Part 4: Procedures for assessment of declared quality levels


Status:
Current
Type:
Standard
Language:
EN
Price from:
€ 74.55

Scope

This part of ISO 3951 establishes sampling plans and procedures by variables that can be used to assess
whether the quality level of an entity (lot, process, etc) conforms to a declared value. The sampling plans have
been devised so that their operating characteristic curves match those of the corresponding attributes plans in
ISO 2859-4 as closely as possible, so that the choice between using sampling by attributes and sampling by
variables is not influenced by attempts to increase the chance of accepting an incorrectly declared quality
level. In this part of ISO 3951, there is a risk of between 1,4 % and 8,2 % of contradicting a correct declared
quality level. The risk is 10 % of failing to contradict an incorrect declared quality level which is related to the
limiting quality ratio (see Clause 4). Sampling plans are provided corresponding to three levels of
discriminatory ability, and for the cases of unknown and known process standard deviation.
In contrast to the procedures in the other parts of ISO 3951, the procedures in this part of ISO 3951 are not
applicable to acceptance assessment of lots. Generally, the balancing of the risks of reaching incorrect
conclusions in assessment procedures will differ from the balancing in the procedures for acceptance
sampling.
This part of ISO 3951 may be used for various forms of quality inspection in situations where objective
evidence of conformity to some declared quality level is to be provided by means of inspection of a sample.
The procedures are applicable to entities such as lots, process output, etc. that allow random samples of
individual items to be taken from the entity.
The sampling plans provided in this part of ISO 3951 are applicable, but not limited, to inspection of a variety
of products such as
— end items;
— components and raw materials;
— operations;
— materials in process;
— supplies in storage;
— maintenance operations;
— data or records;
— administrative procedures.
The procedures are intended to be used when the quality characteristics are measurable variables that are
independent and normally distributed, and where the quantity of interest is the fraction of items that are
nonconforming.

Number of pages: 36

Published: 2011-09-04

Date of approval: 2011-08-24

International relationships : ISO 3951-4:2011 IDT

ICS: 03.120.30 - Application of statistical methods

Item number: M248446


Committees

Committee

  • ISO/TC 69/SC 5/WG 3

Danish committee

DS/S-238

Included in