DOUBLE SAMPLING PLAN

Double sampling plan involves the possibility of putting the decision on the lot until the second sample is taken. The decision of acceptance is based on the result of the two samples combined. In general, the double sampling plan involves less total amount of inspections than involved in the single sampling plan for any protection. It gives second chance to eliminate doubtful lots.

Number of items in the lot = N

First sample size = n₁

First acceptance number = c₁

First rejection number = r₁

Second sample size number = n₂

Second acceptance number = c₂

Number of pieces in two samples combined = n₁ + n₂

The second rejection number both sampling combined = f₂

There are four possibilities for acceptance or rejection of a lot in the method of double sampling.

·        Acceptance after first sample.

·        Rejection after first sample.

·        Acceptance after second sample.

·        Rejection after second sample.