Re: Pick your brains - Use of sampling plans like MIL-STD-105 E or ANSI Z1.4?
O.K - here's some background, then my question(s)
I inherited, many years ago, the Receiving Function. A predecessor had set an AQL on all incoming parts at 0.4%, so on a (usual) lot size of 151 - 280 (letter 'G') we sampled 32, accepted 0 defectives and rejected on 1 defective found. I'm cool with the use of the tables!
I could never get a satisfactory answer on why a 0.4% AQL was chosen and it has bugged me ever since (well, maybe once a year when I indulge in some deja vu of my enjoyable worklife experiences!!)
If I read table X-H-1, on page 46 of the ANSI Z1.4 (1993) doc, I need to reconcile my expected percentage of lots to be accepted 'Pa', with the 'p' value (% non-conforming) of submitted product, to derive my AQL, I think.
So, if I expect that 99% of received product is conforming, then I choose an AQL of 4.0%, and follow the acceptance/rejection rules from table II A (page 12) - I'm actually (statistically) likely to 'see' 3.69% defectives (from estimating on the curve or reading off the table)
Did I get the rationale correct? If so, was it simply a guestimate if the originator of the 0.4% AQL if they couldn't explain what the 'Pa' value was or the impact (risk of the 'p' value), either?
Or am I hosed in my understanding?