6.
Process or Product Monitoring and Control
6.2. Test Product for Acceptability: Lot Acceptance Sampling


Multiple Sampling is an extension of the double sampling concept 
Multiple sampling is an extension of double sampling. It involves
inspection of 1 to \(k\)
successive samples as required to reach an ultimate decision.
MilStd 105D suggests \(k=7\) is a good number. Multiple sampling plans are usually presented in tabular form. 

Procedure for multiple sampling 
The procedure commences with taking a random sample of size \(n_1\)
from a large lot of size \(N\)
and counting the number of defectives, \(d_1\).
If \(d_1 \ge r_1\), the lot is rejected. If \(a_1 < d_1 < r_1\), another sample is taken. 

Efficiency measured by the ASN  Efficiency for a multiple sampling scheme is measured by the average sample number (ASN) required for a given Type I and Type II set of errors. The number of samples needed when following a multiple sampling scheme may vary from trial to trial, and the ASN represents the average of what might happen over many trials with a fixed incoming defect level. 