Acceptable quality level

Acceptable quality level (AQL) is the highest fraction of defective units a sampling plan is designed to pass most of the time — the line a buyer draws for what still counts as an acceptable batch.

FrameworkISO 2859

What it is

See it move

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A sampling plan inspects n = 50 units per batch and accepts it only if none are defective. If the batch's true defect rate sits exactly at an AQL of 1%, the probability all 50 units are good is 0.99 to the power 50, about 60.5%, so roughly 39.5% of batches performing right at the tolerated level are rejected purely by chance.

The formula

LaTeX

P(\text{accept}) = (1 - AQL)^n

Variables

$A Q L$: Acceptable quality level (tolerated defect rate) (%)
$n$: Number of units inspected (sample size) (units)

For a plan that accepts the batch only if the sample contains zero defective units; gives the chance a batch produced exactly at the acceptable quality level still passes inspection.