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America’s incarceration rate is in decline

(www.theatlantic.com)
248 points paulpauper | 3 comments | 25 Jun 25 17:14 UTC | HN request time: 0.675s | source
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mauvehaus ◴[25 Jun 25 17:46 UTC] No.44379970[source]▶

  From the end of World War II until the mid-1970s, the proportion of Americans in prison each year never exceeded 120 per 100,000
That's a funny way of saying 0.12%. Is there a reason for this? It sure doesn't make it easy to compare the numbers they're giving with other numbers given as percentages.

I guess if you're considering a sufficiently small population you could go from ~600,000 people in Vermont * 120/100,000 -> ~720 imprisoned people in Vermont trivially, but we're the second smallest state. This certainly doesn't scale to cities over a million. At least I'd start having to think harder about it.

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everforward ◴[25 Jun 25 18:01 UTC] No.44380130[source]▶
120 per 100,000 includes significant digits. 0.12% could be anywhere from 120-124 per 100,000. You'd really want 0.120%, but that's confusing for different reasons.

Worse would be 1,000 per 100,000, which is 1% but there's no way to tell that it's not rounded or truncated.

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1. ninthcat ◴[25 Jun 25 18:06 UTC] No.44380184[source]▶
"120" and "0.12%" both have 2 significant digits. "120." and "0.120%" have 3 significant digits.
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2. everforward ◴[25 Jun 25 19:14 UTC] No.44380901[source]▶
I would presume, perhaps incorrectly, that “120 per 100,000” has 3 significant digits and “12 per 10,000” has 2.

I’ve never seen a period used like that in census data. It seems like a conscious choice because the period is confusing when used in the middle of a phrase. 12E1 makes more sense but is abnormal notation for many people.

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3. Jtsummers ◴[25 Jun 25 19:22 UTC] No.44380972[source]▶
https://en.wikipedia.org/wiki/Significant_figures

> Trailing zeros in an integer may or may not be significant, depending on the measurement or reporting resolution.

120 is either two or three significant figures, and you can't know which without knowing how the number was arrived at.