Practical Acceptance Sampling (2nd Edition) is a hands-on introduction to the inspection of products and services for quality assurance using statistically-based sampling plans.
The inspection level determines the relation between the batch size and sample size.
Levels I, II, and III are general inspection levels:
Level II is designated as normal.
Level I requires about half the amount of inspection as level II, and is used when reduced sampling cost are required and a lower level of discrimination (or power) can be tolerated.
Level III requires about twice the amount of inspection as level II, and is used when more discrimination (or power) is needed.
The four special inspection levels S-1,S-2,S-3,S-4 use very small samples, and should be employed when small sample sizes are necessary, and when large sampling risks can be tolerated.