Acceptance Sampling - Page 2 of 2: Acceptable Quality Level (AQL)

Acceptance Sampling: LTPD and AQL (Page 2 of 2)

AQL - Acceptable Quality Level

The AQL of a sampling plan is a level of quality routinely accepted by the sampling plan. It is generally defined as the percent defective (defectives per hundred units X 100%) that the sampling plan will accept 95% of the time. This means lots at or better than the AQL are accepted at least 95% of the time and rejected at most 5% of the time.

The AQL can be determined using the operating characteristic (OC) curve by finding that quality level on the bottom axis that corresponds to a probability of acceptance of 0.95 (95%) on the left axis.

Associated with the AQL is a confidence statement one can make. If the lot passes the sampling plan, one can state with 95% confidence that the quality level of the lot is equal to or better than the AQL (i.e., the defective rate of the lot < AQL). On the other hand, if the lot fails the sampling plan, one can state with 95% confidence that the quality level of the lot is worse than the AQL.

The AQL describes what the sampling plan will accept, but it is also important to know what the sampling plan will reject. Information on what the sampling plan will reject is provided by the LTPD of the sampling plan.

Table 2. AQL Sampling Table based on the Mil-STD-105D

	Acceptable Quality Levels for Normal Inspection (% defective)
Lot Size/ Sample Size	.01	.015	.025	.04	.065	.10	.15	.25	.40	.65	1.0	1.5	2.5	4.0
	Lot Acceptance (Ac) Number (maximum number of rejects to accept the lot)
LS=2 to 8 SS=2	0	0	0	0	0	0	0	0	0	0	0	0	0	0
LS=9 to 15 SS=3	0	0	0	0	0	0	0	0	0	0	0	0	0	0
LS=16 to 25 SS=5	0	0	0	0	0	0	0	0	0	0	0	0	0	0
LS=26 to 50 SS=8	0	0	0	0	0	0	0	0	0	0	0	0	1	1
LS=51 to 90 SS=13	0	0	0	0	0	0	0	0	0	0	0	0	1	1
91 to 150 SS=20	0	0	0	0	0	0	0	0	0	0	0	0	1	2
151 to 280 SS=32	0	0	0	0	0	0	0	0	0	0	0	1	2	3
281 to 500 SS=50	0	0	0	0	0	0	0	0	0	0	1	2	3	4
501 to 1200 SS=80	0	0	0	0	0	0	0	0	0	1	2	3	5	7
1201 to 3.2K SS=125	0	0	0	0	0	0	0	0	1	2	3	5	7	10
3201 to 10K SS=200	0	0	0	0	0	0	1	1	2	3	5	7	10	14
10001-35K SS=315	0	0	0	0	0	0	1	2	3	5	7	10	14	21
35001-150K SS=500	0	0	0	1	1	1	2	3	5	7	10	14	21	-
150001-500K SS=800	0	0	0	1	1	2	3	5	7	10	14	21	21	-
	.01	.015	.025	.04	.065	.10	.15	.25	.40	.65	1.0	1.5	2.5	4.0

See also: LTPD; LTPD Table

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