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.