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While I'm sure the methods in here are valuable, the initial claim of 83% seems suspect.

> After launching the Adaptive Audience campaign, CPA for our technical audience went from $34.47 for general remarketing to $18.80 for the targeted remarketing via adaptive audiences, so an 83% overall improvement for CPA for our technical audience – which is a huge win!

This seems like a misleading way to phrase this. When I hear 83% improvement from $34.47, I expect a 83% ($28.61) drop, ie, 34.47 * (1 - 0.83) = 5.86.

This is more reasonably a (34.47 - 18.80) / 34.47 = 45% drop. Still impressive, but not the same.

Is it really standard to express your improvement in these terms? This would make it trivial to have a >100% drop in cost, which is clearly wrong.



Yeah, going from 18.80 to 34.47 would be an 83% increase.

But going from 34.47 to 18.80 is a 45% decrease.

As to your question about whether this is some sort of acceptable alternative way to calculate percentage decrease ... no, this is just a math error.




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