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# standard diviation in biology watch

1. 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
2. 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
3. (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.
4. (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
5. (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.
6. excel wil work out std dev for you.

the formula you need is:

=stdev(cells.... ie a4c4:etc)

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

It calculated std dev against 95% confidence means...
7. (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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