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math guys: how does one figure out a standard deviation

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  • #31
    Originally posted by Lawrence of Arabia
    ah, but you see thats different. thats calculating the number of standarddeviations above the mean a certain number is.

    which has nothing to do with this beauty

    The population standard deviation can be simply calculated as follows:

    1) sum all values
    2) sum the squares of all values
    3) square the result from (1)
    4) Divide (3) by N (the number of values)
    5) Subtract (4) from (2)
    6) Divide (5) by N
    7) Take the square root of (6)

    So, if we have 3, 6, and 7 as values:

    1) = 3+6+7 = 16
    2) = 9 + 36 + 49 = 94
    3) = 16*16 = 256
    4) = 256/3 = 85.33
    5) = 94 - 85.33 = 8.67
    6) = 8.67/3 = 2.89
    7) = SQRT(2.89) = 1.7


    or your refutation that as n increases, sample standard deviation goes to zero.
    I wasn't talking to you there. I was trying to help self.

    Please respond to the post above this one.
    12-17-10 Mohamed Bouazizi NEVER FORGET
    Stadtluft Macht Frei
    Killing it is the new killing it
    Ultima Ratio Regum

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    • #32
      Just because I'm a nice guy, I'll provide you with an excel spreadsheet which does it for 1000 rolls

      The standard deviation (both pop and sample) for those 1000 pseudo-random rolls is provided and is suspiciously close to sqrt(35/12). Rolls are generated by taking a uniform deviate from 0 to 1, multiplying by 6 and taking the ceiling.
      Attached Files
      12-17-10 Mohamed Bouazizi NEVER FORGET
      Stadtluft Macht Frei
      Killing it is the new killing it
      Ultima Ratio Regum

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      • #33
        lawrence

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        • #34
          everyone is right but too stubborn to admit it.
          "I hope I get to punch you in the face one day" - MRT144, Imran Siddiqui
          'I'm fairly certain that a ban on me punching you in the face is not a "right" worth respecting." - loinburger

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          • #35
            No, lawrence doesn't understand the difference between the set and the mean of the set.

            12-17-10 Mohamed Bouazizi NEVER FORGET
            Stadtluft Macht Frei
            Killing it is the new killing it
            Ultima Ratio Regum

            Comment


            • #36
              This thread makes me cry. Is LoA really about to get a degree in economics?

              Comment


              • #37
                Yes.
                12-17-10 Mohamed Bouazizi NEVER FORGET
                Stadtluft Macht Frei
                Killing it is the new killing it
                Ultima Ratio Regum

                Comment


                • #38
                  Originally posted by KrazyHorse
                  No, lawrence doesn't understand the difference between the set and the mean of the set.

                  hes like a kid with all the legos but no schematic to build something with.
                  "I hope I get to punch you in the face one day" - MRT144, Imran Siddiqui
                  'I'm fairly certain that a ban on me punching you in the face is not a "right" worth respecting." - loinburger

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                  • #39
                    Like I said, it's the same way with the kids I TA. They cram a bunch of information into their head, but don't know what any of it means.

                    12-17-10 Mohamed Bouazizi NEVER FORGET
                    Stadtluft Macht Frei
                    Killing it is the new killing it
                    Ultima Ratio Regum

                    Comment


                    • #40
                      I don't know any of my TA's.

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                      • #41
                        They spoil the kids at Hopkins. We're combination graders, tutors and assistant professors.
                        12-17-10 Mohamed Bouazizi NEVER FORGET
                        Stadtluft Macht Frei
                        Killing it is the new killing it
                        Ultima Ratio Regum

                        Comment


                        • #42
                          I knew my students when I cared. After the first year, I didn't.

                          I was freinds with my undergrad professors. My graduate school professors I mostly didn't know (except some of the old school ones).

                          Jon Miller
                          Jon Miller-
                          I AM.CANADIAN
                          GENERATION 35: The first time you see this, copy it into your sig on any forum and add 1 to the generation. Social experiment.

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                          • #43
                            Originally posted by KrazyHorse
                            They spoil the kids at Hopkins. We're combination graders, tutors and assistant professors.
                            They should keep the kids away from the TAs. If you're any indication, ta's are mostly just condescending ass hats.

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                            • #44
                              no, you have it messed up again. heres what I get.

                              standard deviation sample = squarroot(Var(X_bar)/n)
                              in this case, var(X_bar) is 2.89/1000 = 0.00289.
                              the standard deviation of the sample is squarrout(0.00289) = 0.054, which is close to zero.
                              "Everything for the State, nothing against the State, nothing outside the State" - Benito Mussolini

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                              • #45
                                standard deviation sample = squarroot(Var(X_bar)/n)


                                You are an idiot.
                                12-17-10 Mohamed Bouazizi NEVER FORGET
                                Stadtluft Macht Frei
                                Killing it is the new killing it
                                Ultima Ratio Regum

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