# Standard deviation

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#1
i have the basic forumla for s.d.- i can work it out on the computer, by hand, in my sleep etc.

but for my stats coursework i need to prove something has a normal distribution and i do this by finding one standard deviation from the mean, then 2 and then 3. but i don't how to do that...

can anyone help at all? rep will be plentiful for anyone who obliges *although brownie points do go to those who, albeit unsuccesfully, tried to help me in the academic bit*

lou xxx
0
17 years ago
#2
(Original post by lou p lou)
finding one standard deviation from the mean, then 2 and then 3.
what do you mean by this bit?
0
17 years ago
#3
(Original post by lou p lou)
i have the basic forumla for s.d.- i can work it out on the computer, by hand, in my sleep etc.

but for my stats coursework i need to prove something has a normal distribution and i do this by finding one standard deviation from the mean, then 2 and then 3. but i don't how to do that...

can anyone help at all? rep will be plentiful for anyone who obliges *although brownie points do go to those who, albeit unsuccesfully, tried to help me in the academic bit*

lou xxx
between mean - (3*stdev) and mean + (3*stdev)
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#4
(Original post by elpaw)
what do you mean by this bit?
that's my problem, i don't really know. my teacher was just like 'test for normality by finding 1 s.d. from the mean and then 2 and then 3'

the only help i can give is that i know a certain percnatge of all data should be within 1 s.d. and by 3 s.ds about 98% of all the data should be included.

but i really am incredibly vague on what the hell i'm meant to be doing *and my teacher is really unapproachable*

argh!!!!!!!

lou xxxx
0
17 years ago
#5
(Original post by lou p lou)
that's my problem, i don't really know. my teacher was just like 'test for normality by finding 1 s.d. from the mean and then 2 and then 3'

the only help i can give is that i know a certain percnatge of all data should be within 1 s.d. and by 3 s.ds about 98% of all the data should be included.

but i really am incredibly vague on what the hell i'm meant to be doing *and my teacher is really unapproachable*

argh!!!!!!!

lou xxxx

EDIt: on this site http://www.robertniles.com/stats/stdev.shtml
0
17 years ago
#6
(Original post by lou p lou)
that's my problem, i don't really know. my teacher was just like 'test for normality by finding 1 s.d. from the mean and then 2 and then 3'

the only help i can give is that i know a certain percnatge of all data should be within 1 s.d. and by 3 s.ds about 98% of all the data should be included.

but i really am incredibly vague on what the hell i'm meant to be doing *and my teacher is really unapproachable*

argh!!!!!!!

lou xxxx
Does your teacher want to check that you haven't got a skewed distribution? ie a "normal" distribution would be symmetrical around the mean, A skewed distribution would show a distinct bias.
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#7
(Original post by me!)

EDIt: on this site http://www.robertniles.com/stats/stdev.shtml
ooooh, that kinda helps.

me thinks i'm going to have to dig out every piece of stats info i have on s.d. *looks at horrible pile of notes + textbooks + revision guides + psychology stats books....*

cheers everyone.

lou xxx
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