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Absolutely cite any hard numbers you use. It's good practice and not nearly common enough, which means it should be encouraged. Given how quickly statistics become outdated, I would definitely cite...
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#3: Attribution notice added
Source: https://writers.stackexchange.com/a/12597 License name: CC BY-SA 3.0 License URL: https://creativecommons.org/licenses/by-sa/3.0/
#2: Initial revision
Absolutely cite any hard numbers you use. It's good practice and not nearly common enough, which means it should be encouraged. Given how quickly statistics become outdated, I would definitely cite at least the year of the study/article/whatnot. On Wikipedia some editors would include the date of publication and also _date accessed_, which is relevant to web sources. I don't think that's mandatory, though. Use it if you have reason to believe the source is likely to be edited, e.g. a blog post.