Acceptance Sampling by Attributes - Compare

User Defined Plans - Average Outgoing Quality (AOQ)

  

The average outgoing quality level represents the relationship between the quality of the incoming material and the quality of the outgoing material, assuming that rejected lots will be 100% inspected and all defective items will be replaced or reworked.

As the defect level of the incoming parts increases, the inherent quality of the accepted lots decreases; however, the number of rejected lots also increases. The sorting of the bad parts (100% inspection and removal) helps the outgoing quality level, but at a high cost. The maximum possible defect level, an important characteristic of the sampling plan, is the average outgoing quality limit (AOQL).

Example Output

Compare User Defined Plan(s)

 

 Sample  Acceptance    Percent  Probability  Probability

Size(n)   Number(c)  Defective    Accepting    Rejecting    AOQ      ATI

    150          10          2        1.000        0.000  1.988    155.9

    150          10          5        0.868        0.132  4.313   3435.6

 

    200          10          2        0.997        0.003  1.979    262.8

    200          10          5        0.583        0.417  2.892  10539.9

 

    250          10          2        0.987        0.013  1.955    566.7

    250          10          5        0.291        0.709  1.440  17799.6

 

 

 Sample  Acceptance         At Percent

Size(n)   Number(c)   AOQL   Defective

    150          10  4.355       5.369

    200          10  3.254       4.027

    250          10  2.595       3.222

 

Accept lot if defective items in n sampled ≤ c;  Otherwise reject.

Interpretation

For the grocery bags, when the average incoming quality level is 2%, the average outgoing quality is close to 2% - 1.988%, 1.979%, and 1.955% defective, when the sample sizes are 150, 200, and 250 and the accept number is 10. When the average incoming quality level is 5%, the average outgoing quality 4.313%, 2.892%, and 1.440% defective, when the sample sizes are 150, 200, and 250 and the accept number is 10.

Keeping the accept number at 10:

·    When the sample size is 150, the AOQL is 4.355% defective.

·    When the sample size is 200, the AOQL is 3.254% defective.

·    When the sample size is 250, the AOQL is 2.595% defective.

As the sample size decreases, the number of rejected lots with all defects removed also decreases, so the quality gets worse. This results in a higher average outgoing quality limit.