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Simple explanations of how to do Spearman Rank & Standard Deviation Please? Watch

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    Just wondering if someone could explain how to do the Spearman Rank and Standard Deviation techniques in the simplest way possible?
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    Here's standard deviation:

    You start with a load of data like:
    34 45 56 23 79
    (If you don't, and you start with a frequency table or something, let me know because you have to do different stuff for that!)

    Square each number:
    1156 2025 3136 529 6241

    Now add all of the above together:
    13087

    And then divide how many there are:
    2617.4

    Moving on, now find the mean average of the original data (add them and divide by number of them):
    47.4

    Square it:
    2246.76

    Now take this number (2246.76) from the number we calculated before (2617.4) to get:
    370.64

    And finally, square root it:
    19.252 (to 5.s.f.)


    So:

    Square
    Add
    Divide by n

    Average of original data
    Square
    Take
    Root
    Omg i just found the standard deviation!

    Spoiler:
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    If you can't remember which one to take from which on the "Take" step, then just think it's the one which gives a positive answer!
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    (Original post by Lou Reed)
    They're both long-winded and boring to calculate, so no simple ways really.

    For SD, i remember it as "sum of x squared over n", that's not all you do, here are the steps for a frequency table;
    - square x to get x^2
    - times frequency by corresponding x^2
    - sum this
    - divide by n
    - minus the mean squared (i'm sure you know how to work out mean)
    - square root it

    For SR, the equation is really self-explanatory:



    - find differences between the data
    - square them
    - sum them
    - times by 6
    - divide answer by (n(n^2 - 1))
    - take answer away from 1

    Does that help?
    Seems to, just give me a bit to get my head round it lol.
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    (Original post by placenta medicae talpae)
    Here's standard deviation:

    You start with a load of data like:
    34 45 56 23 79
    (If you don't, and you start with a frequency table or something, let me know because you have to do different stuff for that!)

    Square each number:
    1156 2025 3136 529 6241

    Now add all of the above together:
    13087

    And then divide how many there are:
    2617.4

    Remember this number!
    Write it down or something

    Moving on, now find the mean of the original data (add them and divide by number of them):
    47.4

    Square it:
    2246.76

    Now take this number (2246.76) from the number we calculated before (2617.4) to get:
    370.64

    And finally, square root it:
    19.252 (to 5.s.f.)
    Nice explanation

    How would I calculate it for data on a frequency table then?
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    (Original post by sandeep90)
    Seems to, just give me a bit to get my head round it lol.
    Oh, erm, about this one - it's important that it's the ranks which have to be considered, rather than the actual values!
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    (Original post by sandeep90)
    Nice explanation

    How would I calculate it for data on a frequency table then?
    Cheers - I edited it a bit, so it's much clearer now

    To be honest, the formula is pretty much the same:
    I just think of it as "stick an f before the x".

    So instead of being:
    \sigma = \sqrt{\frac{\sum x^2}{n}-\bar{x}^2}

    It is now:
    \sigma = \sqrt{\frac{\sum f x^2}{n}-\bar{x}^2}

    Spoiler:
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    If you prefer the alternative formula, then instead of being:
    \sigma = \sqrt{\frac{\sum (x-\bar{x})^2}{n}}
    It is now:
    \sigma = \sqrt{\frac{\sum f(x-\bar{x})^2}{n}}


    And here, f.x^2 is the value representing a class, squared, and then timesed by the frequency of that class - how many values lie therein.
    I appreciate that might be a little vague; let me know if it needs to be clarified.

    I think that (surprisingly) the hardest bit of this is remembering how to find the mean from the frequency table!

    \bar{x}=\frac{\sum x}{n}
 
 
 
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