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Sampling Plan Analyzer Help System 

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LTPD - Lot Tolerance Percent Defective

The LTPD of a sampling plan is a level of quality routinely rejected by the sampling plan. It is generally defined as that level of quality (percent defective, defects per hundred units, etc.) that the sampling plan will accept 10% of the time. This means lots at or worse than the LTPD are accepted at most 10% of the time. In other words, they are rejected at least 90% of the time. The LTPD can be determined using the OC curve by finding that quality level on the bottom axis that corresponds to a probability of acceptance of 0.10 (10%) on the left axis.

Associated with the LTPD is a confidence statement one can make. If the lot passes the sampling plan, one can state with 90% confidence that the quality level (defective rate, etc.) is below the LTPD. In other words, passing the sampling plan demonstrates that the LTPD has been meet.

The probability of acceptance at the LTPD can be reset using the
Definitions of AQL and LTPD dialog box. The associated confidence statements are also displayed in this dialog box.


The LTPD is used to help describe the
protection provided a sampling plan. But it only provides half the answer. It describes what the sampling plan will reject. We would also like to know what the sampling plan will accept. The answer to this second question is provided by the AQL.

Equivalent terms commonly used instead of LTPD are:
  • LQ
  • RQL
  • UQL