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Steps of getting standard deviation. http://www.techbookreport.com/tutorials/stddev-30-secs.html:

  1. Work out the average (mean value) of your set of numbers

  2. Work out the difference between each number and the mean

  3. Square the differences

  4. Add up the square of all the differences

  5. Divide this by one less than the number of numbers in your set - this is called the variance

  6. Take the square root of the variance and you've got the standard deviation

Am I missing out something, or why do we need to square the differences in step 3?

Why not simply do a Abs (multiply all negative numbers by -1) in step 3?

Also, my second question is why do we need to divide by one less than the number of numbers in the set in step 5? why not simply divide by the number of numbers?

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    Overheard: "If the difference between $n$ and $n-1$ ever matters to you, then you are probably up to no good anyway; e.g. trying to substantiate a questionable hypothesis with marginal data."2011-09-03

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