This British Standard gives guidance on the selection of an acceptance sampling system, scheme or plan for inspection by variables. It does this principally by reviewing the available systems specified by various British Standards and showing ways in which these can be compared in order to assess their suitability for an intended application. It is assumed that the choice has already been made to use sampling by variables in preference to sampling by attributes.
The guidance in this British Standard is confined to acceptance sampling of products that are supplied in lots and that can be classified as consisting of discrete items (i.e. discrete articles of product). Each item in a lot can be identified and segregated from the other items in the lot and has an equal chance of being included in the sample. Each item of product is countable and has specific characteristics that are measurable on a continuous scale. Each characteristic has, at least to a good approximation, a normal distribution or a distribution that can be transformed so that it closely resembles a normal distribution.
Standards on acceptance sampling by variables are applicable to a wide variety of inspection situations. These include, but are not limited to, the following:
a) end items, such as complete products or sub-assemblies;
b) components and raw materials;
c) services;
d) materials in process;
e) supplies in storage;
f) maintenance operations;
g) data or records;
h) administrative procedures.
Although this British Standard is written principally in terms of manufacture and production, this should be interpreted liberally as it is applicable to the selection of sampling systems, schemes and plans for all types of product and processes as defined in BS EN ISO 9000.