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Acceptable Quality Level (AQL); used in
sampling inspection, the maximum percentage
of defectives that is acceptable as a long-term
average. See also OC Curve.
See Acceptable Quality Level.
Used in sampling inspection. It is the
risk that a consumer will accept a batch
of worse quality than the Limiting Quality
Level. It is equivalent to a Type II Error.
See also OC Curve.
LQL. Used in sampling inspection. It is
the proportion of nonconforming items associated
with the consumer’s risk. It can be
regarded as the minimum quality that the
customer would not want to accept, even
for a single batch. The AQL is the minimum
acceptable long term average. See also OC
Curve.
See Limiting Quality Level.
Lot Tolerance Percent Defective. The Limiting
Quality Level expressed as a percentage.
Curves that show the probability of accepting
a batch over a range of proportions of nonconforming
items. The figure shows an 'OC' (Operating
Characteristic) Curve for a sample if 50
taken from a batch of 2000 and using a critical
acceptance number 'c' of 2.
Note that OC Curves are also used other
than in sampling inspection. They are used
to find the Average Run Length in control
charts.
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Characteristic Curve |
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See OC Curve.
Used in sampling inspection. It is the
probability that a batch with a quality
equal to, or better than, the AQL will be
rejected. It is equivalent to the Type I
error. See also OC Curve.
To avoid calculation, and negotiation,
published standard sampling plans are normally
used for inspection. The most commonly accepted
being ANSI/ASQ Z1.4-2003.
The figure shows an example of a page from
a sampling plan:
The first step is to find
the sample size code letter. This is obtained
from a separate table and is based on the
lot size and the severity of the inspection
required. A value for the AQL is also selected.
The table shown above is then
used to find the sample accept/reject values.
For example if the code letter were 'N'
and the AQL was 0.15 then the sample size
would be 500. The batch would be accepted
if there were 1 defect or less, and rejected
if there were two defects or more.
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