Statistics Formula: Where did it come from?

  1. Hi, I have just started my AP Stats class and we have a short quiz tomorrow on a few things. I was just wondering where did this formula come from? Where did those numbers come from to create that forumula?
     
  2. jcsd
  3. mathman

    mathman 6,395
    Science Advisor
    Gold Member

    This may not answer your question completely. However the mathematical expectation (theoretical average) of s2 is the theoretical variance of the statistical average.
     
  4. lurflurf

    lurflurf 2,325
    Homework Helper

    This will not be completely answer it but
    In statistics the idea is to get a picture of how lots of numbers act by using a few numbers. The first statistic often used is the mean
    mean=sum/number
    If our data has mean 0 we might like to know are all the numbers zero, most, maybe half are 1000000000 and half -1000000000. We want an idea of spreadoutness. so we consider
    mean(x-mean(x))
    but it is zero we cure that with
    mean((x-mean(x))^2)
    but we are using n numbers like n+1 (mean(x) depends on x hence is not its own number)
    so we do
    (n/(n-1))mean((x-mean(x))^2)
    but it is squarey so
    sqrt((n/(n-1))mean((x-mean(x))^2))
    which is the standard deviation we know and love
     
  5. That helps thx. I now get most of the formula except why is it (n-1)?
     
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