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Comment by bilbo-b-baggins | Hacker News Reader

Doesn’t 15-fold mean multiplied by two 15 times, or 32,000x not 15x?

I feel like someone should have caught that before publication.

No https://en.m.wikipedia.org/wiki/Fold_change

I’ve not heard the term used that way—I’ve always understood it to indicate a multiple. But now that you’ve said it, the idea of -fold as “folding something in half” is interesting to think about!

I imagine folding too. But then we couldn’t ever achieve more than maybe a twelve-fold increase.

I don't know if the engineering field has the same conventions, but in biology we use "fold" as it was used in the paper. When comparing the signal of two things, the fold change is how many times one is bigger than the other (basically A/B). If A is 15-fold higher than B then it's 15x B.

What you described is the Log2 Fold Change (log2(A/B)), meaning that if A has a log2FC of 15 over B, its signal is 2^15 times higher, hence ≈32,000x.

I'm bummed that you're getting downvoted for what's IMO a very natural question, especially given that "times" is unambiguous and that folding naturally implies a doubling. But this is English, it's deliberately designed to not make sense (see also the modern definition of "literally").

mumbles something else about 2^15

I think its getting downvoted because they suggested that the article's copyeditor should have caught it, despite the article being right. I doubt they would have been downvoted if they just asked, but suggesting that someone failed at their job despite them actually doing it correctly tends to get people a bit uppity.

Words are arbitrary, but there really isn't any dispute what -fold means as a suffix. See the dictionary entry for it https://www.merriam-webster.com/dictionary/-fold

Also as far as i know, this isn't just an english being weird thing, most germanic languages use "fold" the same way.

> folding naturally implies a doubling.

Why is that? I can imagine doing two folds on a sheet of paper and ending up with three layers of paper. Imo one fold adds one layer.

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