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Glossary “A” Definition of Terms

α (alpha) Risk

The maximum probability of saying a process or lot is unacceptable when, in fact, it is acceptable. See also Producer’s Risk.

Acceptable Quality Level (AQL)

When used in acceptance sampling: the maximum percentage or proportion of nonconforming units which can be considered acceptable as a process average.

Acceptance Sampling 

Sampling inspection in which decisions concerning acceptance or rejection of materials or services are made. Also includes procedures used in determining the acceptability of the items in question based on the results of the inspection.

Accuracy (of measurement)

Difference between the average result of a measurement with a particular instrument and the true value of the quantity being measured.

ANSI/ASQC Z1.4-1993

A set of specifications for acceptance sampling plans based on acceptable quality level (AQL). For a given AQL, lot size, and level of inspection, the specification lists the number of defective units that is acceptable, and the number that requires rejection of the lot. The specifications allow for tightening or relaxing of inspection requirements based on previous inspection results.

AOQ (Average Outgoing Quality) 

The expected average outgoing quality following the use of an acceptance sampling plan for a given level of quality. Any lots not meeting this level of quality must be inspected, and nonconforming units removed and replaced. These lots are then included with the acceptable lots.

AOQL (Average Outgoing Quality Limit)

 For a given set of sampling criteria (sampling plan), the maximum AOQ over all possible levels of incoming quality.

Assignable Causes (of variation)

Significant, identifiable changes in the relationships of materials, methods, machines, and people.

Attribute Data (quality)

Data coming basically from GO/NO-GO, pass/fail determinations of whether units conform to standards. Also includes noting the presence or absence of a quality characteristic. May or may not include weighting by the seriousness of defects, etc.


a number that is calculated by adding quantities together and dividing the total by the number of quantities. See also mean 

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