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What does the size of the standard deviation mean?

For example, if I want to study human body size and I find that adult human body size has a standard deviation of 2 cm, I would probably infer that adult human body size is very uniform, while a 2 cm standard deviation in the size of mice would mean that mice differ surprisingly much in body size.

Obviously the meaning of the standard deviation is its relation to the mean, and a standard deviation around a tenth of the mean is unremarkable (e.g. for IQ: SD = 0.15 * M).

But what is considered "small" and what is "large", when it comes to the relation between standard deviation and mean? Are there guidelines similar to the ones that Cohen gives for correlations (a correlation of 0.5 is large, 0.3 is moderate, and 0.1 is small)?

  • You already asked this, and got answers! If you dont like the answers, then say so on that old question (and explain why). You should not simply ask again! – kjetil b halvorsen Sep 08 '15 at 12:54
  • Actually I'm getting a bit angry right now. As I learned through the comments to my other question, I was asking that question the wrong way. So I edited the question, but glen_b, who is a moderator for this site, explained that that would be impolite because it made the questions that had been given invalid. He suggestwd to me I ask a new question, which I did. But now you folks delete this question because it is a duplicate and whuber gives comments to my old question which are useless to me because that question does not actually ask what I want to know. So what can I do? –  Sep 08 '15 at 16:46
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    I can appreciate why this circumstance would frustrate you. In defense of this community, I think if there is any inconsistency in how your questions are being treated it is because (a) you are asking multiple questions per post and (b) you have now created three threads focusing on almost identically phrased questions. We could use your help in sorting this all out so that we don't act inconsistently or mistakenly. In particular, you can (1) limit the scope of each thread, (2) make cross-references to your related threads, and (3) work to improve each post rather than creating near copies. – whuber Sep 08 '15 at 17:25
  • I really don't understand this enough to format my question according to your understanding of the matter. To me the different questions appear unrelated, otherwise I wouldn't have posted them as separate questions. An answer would help me understand. –  Sep 09 '15 at 06:31

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