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standard diviation in biology watch

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    can any1 help plz i have to do standard divation of the results but no idea wot to do.
    im basically testing antibiotics against bacteria ie

    e coli against novobiocin
    ecoli against amoxicillin
    s albus against novobiocin
    s albus against amoxicillin

    so i have 4 sets of results from the above and have worked out the mean so have 4 means.
    i also have added up the class results and i have 4 means for the class result as well.

    my means are:

    e coli against novobiocin 13
    ecoli against amoxicillin 15.3
    s albus against novobiocin 19.6
    s albus against amoxicillin 14.1

    the class means including mine are

    e coli against novobiocin 13.5
    ecoli against amoxicillin 15.0
    s albus against novobiocin 18.7
    s albus against amoxicillin 14.5

    how wud i do standard diviation frm these results i'll give whoever can help rep :cool:
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    Hey, i never thought S1 maths would be useful.. well it isnt but here goes..

    this website says it all: http://www.bbc.co.uk/education/asgur...inciples.shtml

    but in general,
    there are 2 formulae for standard deviation but i prefer to use this one:

    S.D. = square root of ( sum of all s(x^2) - mean^2)

    where ^2 means raise to power 2..

    in your case i think, each x value would represent the equivalent value on x-axis..(your set values of bacteria growth) and s would represent the number of times you got each x variable. And you have to add up all of the possible s(x^2) for every x value you got, then take away mean squared and then square root the answer.

    Its pretty difficult to understand, but i hope this helps.. Laterzz
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    (Original post by Nijman)
    Hey, i never thought S1 maths would be useful.. well it isnt but here goes..

    this website says it all: http://www.bbc.co.uk/education/asgur...inciples.shtml

    but in general,
    there are 2 formulae for standard deviation but i prefer to use this one:

    S.D. = square root of ( sum of all s(x^2) - mean^2)

    where ^2 means raise to power 2..

    in your case i think, each x value would represent the equivalent value on x-axis..(your set values of bacteria growth) and s would represent the number of times you got each x variable. And you have to add up all of the possible s(x^2) for every x value you got, then take away mean squared and then square root the answer.

    Its pretty difficult to understand, but i hope this helps.. Laterzz
    hey thanks its just coz ive got 4 means therefore 4 different results im not sure whether id need to do 4 standard diviations.
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    (Original post by emmz)
    hey thanks its just coz ive got 4 means therefore 4 different results im not sure whether id need to do 4 standard diviations.
    any1 know
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    (Original post by emmz)
    any1 know
    You would have to calculate four different ranks for the values. As you are comparing 4 sets of data.

    Regards.
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    excel wil work out std dev for you.

    the formula you need is:

    =stdev(cells.... ie a4:b4:c4:etc)

    where the brackets are, drag the cusor along the cells with your data in

    It calculated std dev against 95% confidence means...
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    (Original post by Bhaal85)
    You would have to calculate four different ranks for the values. As you are comparing 4 sets of data.

    Regards.
    yes im comparing the 4 sets of data. would i have to do 4 standard diviations though.
    soz i know how thick i sound lol
 
 
 
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