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FOOD AND DRUG ADMINISTRATION - page 88 / 263

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idea of what's going on.  If we had an ideal test here, we'd have the magenta line in the center.  So this is looking at the first tier actually of the two-tier test with 24 samples in the first tier, and the target here is 2.5 percent consumer risk, not 5.  So ideally, we'd have 2.5 percent all the way along as the mean goes from 75 percent to 125 percent of label claim.  The blue curve shows you the old standard normal theory of tolerance intervals, what it does.  It's nicely right in the center but drops off very quickly.  And I had alluded earlier to statistical conservatism in the normal theory tolerance intervals and that's what that is.  This gap between the blue and the purple is something you'd like to do away with and because you're increasing the producer risk here by making the consumer risk less than it needs to be.

Now, the problem is that, depending on your choice of constants, using the approach of the IPAC, you can end up with things that look like this, so this goes, instead of the 2.5 percent where it should be, up above 4 percent here and coming back down.  Now, again remember, this was all based on the 2001 report and they've changed their constants since then.

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