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I have been going in rounds with this problem... I may be thinking "complicated", any advice?

I have the mean and total sample size (=number of data points) and I need to know what is the standard deviation (SD).

I know I can calculate back the sum of individual scores from the formal formula for calculation of the mean, i.e.:

$M = \frac{\Sigma X}{N}$

where X=individual data points N=number of data points

However after this step I am stuck. To find the SD using the variance I need to know the individual data points and which I don't have.

I then end up with two "unknown" variables, $S^2$ and $X$ in this formula:

$S^2 = \frac{\Sigma(X-M)^2}{N - 1}$

Thanks!


Thank you André and Jonathan. I now got some extra information: I am given the N and mean(maximum), e.g.: N=596, mean(maximum): 5.86(39.1); any extra advice?

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    You are stuck. If the data points are all equal (they might be) your sample variance would be $0$. If they wiggle all over the place, the sample variance would be high.2012-12-01
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    What do you mean by "mean(maximum)"?2012-12-01

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