# Talk:Standard deviation

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Field: Probability and statistics
One of the 500 most frequently viewed mathematics articles.
WikiProject Statistics (Rated C-class, Top-importance)

This article is within the scope of the WikiProject Statistics, a collaborative effort to improve the coverage of statistics on Wikipedia. If you would like to participate, please visit the project page or join the discussion.

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## General comment this and other main stats pages.

I am re-teaching myself stats through reading many of these articles.

I have seen a lot of "improvements" to the stats pages on basics like standard deviation over the last few years. I have valued the excellent graphics that have been developed. I have also valued the sections with a rigorous mathematical equation based discussion of relevant issues.

In the process of these improvements though, I have felt that the wording of the introductory sections to many of these articles has become more complicated in the language trying to ensure exactness in initial concept, including boundaries, nuances and exceptions to the basic concept. All in the one paragraph.

If you already understand the topic, then this precision of definition all makes sense. However most people are seeking a beginning understanding, and in this regard the precision adds to many things to keep track of in getting the basic concept. Reading these intro sections, often I now find it difficult to get the basic "jist" of it. My response has been, nope don't get it, to hard, too complicated. Just can not get my head around it.

I have not edited the intro sections myself as I can see a lot of thought and care has gone into them to ensure they are correct in the full detail of the concept being introduced. However I do suggest consideration be given to much lighter simpler laymans style description to basic concepts that may not be that precise, but does convey the jist and feel of the basic concept.

I present the issue as I have experienced it, but I do not have the skills to write what is needed. I think such intro paragraphs are better written by those who have a conceptual understanding but not a detailed technical mathematical understanding of the topic.

So first a laymans very basic jist of the concept as an intro paragraph.

Then a more refined, technically correct refinement of the concept, followed by various diagramatic and more focused expansion on aspects of the concept. Some basic examples perhaps in the most basic form.

Then for those who want to technically use and apply these concepts and do the statistics in practice, the more rigorous and mathematical discussions of the topic and subtopics. For those already familiar with the concept the rigorous mathematical explanation of various aspects is an excellent and important part of Wikipedia in my view.

With this page, I think the coverage of combining samples does belong on this page. The same topic may also belong on the other page as well. Certainly I looked for it here. CitizenofEarth001 (talk) 11:01, 16 August 2014 (UTC)

I agree with Citizen, not only for statistics-related articles but many others on topics involving complex mathematical operations, there is a real lack of simple, high-level conceptual description of the concept in terms comprehensible to readers not already well-versed in the topics. To use a personal example: I really like fractals, I like to look at them and appreciate their visual appeal and self-similarity properties, and while I understand and appreciate that they are produced by mathematical calculations involving imaginary and complex numbers (concepts I generally grasp), I'm not familiar with the majority of the technical terms used in some of the more detailed aspects. I recall one time I was reading a fractal-related article that mentioned Misiurewicz points. Unfamiliar with that term, I followed the link hoping to learn enough to provide a frame of reference for the context in the previous page, but that entire article was so completely filled with either formulae or sentences containing so many other unfamiliar terms that it was hopeless for me unless I wanted to spend hours diving through one article after another to become a fractals expert! (That article has since been improved somewhat; there is a semi-decent lay explanation near the bottom.)
So anyway, I came to this page not knowing what a standard deviation is except that it relates to a set of values in some way. Now I know that a smaller standard deviation means that the values in the set tend to be closer together than a larger standard deviation, but I still don't conceptually understand what "one standard deviation" really means - I mean, if you tell me x and y are one standard deviation apart, I could refer to this page, and work out some math, and figure out the quantitative difference between x and y, but I still don't get it. What is the significance of the fact that they are one standard deviation apart? How does it relate to whatever else was being talked about immediately beforehand? It's still just a vague, abstract "thingy" to me.
Sorry for going on so long about this, I feel like I've come across as dumb, which is partly due to the fact I'm typing this on my phone, which is slow, cumbersome, and prone to errors, this preventing me from fully expressing all the thoughts I'd like to, but the key point I'm trying to make is, yes, please continue to develop broad conceptual explanations on this and other articles. Thanks.
Dansiman (talk|Contribs) 18:01, 30 January 2015 (UTC)
These are very helpful comments. I agree that the art of writing an encyclopedia article for Wikipedia is to keep the article approachable for a beginner while also making it scrupulously accurate. That's an art well worth practicing, and I hope to devote some time to improving this article precisely along those lines. -- WeijiBaikeBianji (talk, how I edit) 21:50, 30 January 2015 (UTC)

## SD per AMA and others

A few weeks ago an anon was desperate to convince everyone that the "SD" abbreviation shouldn't be used for standard deviation. Anyone who ever used PubMed to an appreciable extent knows that that's a misapprehension (no matter how well-intentioned). I just wanted to explain here that AMA style is one of various styles that uses "SD". The anon's change was reverted (a good thing), but no one took the time to explain to them why (a regrettable thing). So I just remembered to explain here. Quercus solaris (talk) 22:43, 16 March 2015 (UTC)

## Neither n nor n-1

What about dividing the sum of the squared differences by something that is neither n nor n-1, e.g. n-2? GeoffreyT2000 (talk) 04:36, 30 April 2015 (UTC)

## n vs. n-1

Is there a difference between dividing by n and dividing by n-1? GeoffreyT2000 (talk) 04:40, 30 April 2015 (UTC)