A quick post today on a topic that I see often:  incorrect specifications for potency assays.

It is fairly common to see specifications for a potency assays that look like this:
50% – 150%
80% – 120%
Etc…

What is the problem with these?  While they look to be symmetrical around 100% they are not.  Percentages are ratios, and therefore, the correct specifications should actually be:
50% – 200% (1/2 to 2/1)
80% – 125% (4/5 to 5/4)

Of course, the top set of specifications may actually be deliberately asymmetrical (for safety reasons on the high end for example), but in most cases I’ve seen they are simply listed this way by mistake.

Thanks for reading,

Dan

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