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Single Sampling Plan for Defects Per Unit

Characteristic:

Defects per unit

Assumptions:

(1) Representative sample

Parameters:

n = sample size, integer satisfying n>0
a = accept number, integer satisfying a³0

Sometimes a third parameter, r = reject number, is given.  The parameter r is always equal to a+1 and is redundant.

Procedure:

(1) Take a representative sample of n units from the lot to be inspected.
(2) Count the number of defects in the sample.
(3) If this count is less than or equal to a, accept the lot.  Otherwise reject the lot.

Sometimes the accept or reject decision is determined before all units are inspected.  In this case, the inspection can be curtailed.  For single sampling plans for defects you can only curtail on rejection as follows:

Curtail on Rejection:  Stop the inspection and reject as soon as a+1 defects are found.