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Math Help - Help finding percentiles.

  1. #1
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    Help finding percentiles.

    Hi;
    Lets say I have a list of values 1 2 3 4 5 6 7 8 9 10.
    and I want to find the 20percentile I whould do this.

    20/100*10=2 position two which just happens to have the value of 2 thats fine.


    Now lets say I have this list of values 1 2 3 4 5 6 7 8 9
    and I want to find the 20 percentile I whould do this.

    20/100*9=1.8 because this now produces a decimal do just round up to position two
    which just happens to have the value of 2.

    because if I find the average of the first ad secund value I get a decimal again ie 1.5.

    Conclution: If theres an even number of values just take that value and if theres an odd
    number of values round up and take that value?

    Thanks.
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  2. #2
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    Re: Help finding percentiles.

    Hey anthonye.

    You need to get the actual value that corresponds to the particular percentile.

    So basically you need to find P(X <= x) = a for some x given a value of a (20th percentile implies a = 0.2).
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  3. #3
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    Re: Help finding percentiles.

    Thanks Chiro;
    I know I need to find the value of a particular percentile,What I need to know
    is am I using the correct process to find a percentile.
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  4. #4
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    Re: Help finding percentiles.

    First you rank the observations in ascending (increasing) order and find the probability distribution (from the frequency table).

    Once you have done this then you find the x such that P(X <= x) = a where a is your percentile.

    This is the general method for finding percentiles.
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