Calculate 2 standard deviations

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Chris on 28 Aug 2011
Commented: Thomas To on 20 Jan 2020
I am trying to calculate +/- two standard deviations from the mean of a bunch of values. I am not sure if I am using the standard deviation function properly. Would I just multiply by two to get 2 standard deviations?
dmean = mean(values(:,1)); upperstd = dmean+2*std(values(:,1)); lowerstd = dmean-2*std(values(:,1));

Accepted Answer

Wayne King
Wayne King on 28 Aug 2011
Hi Chris, for a matrix of data
x = randn(10,4);
gives the sample means of the columns plus/minus 2 times the standard deviation. The question is whether you really want the sample standard deviation here, or the standard error of the mean.
Thomas To
Thomas To on 20 Jan 2020
Jay, the standard error is calculated by taking the standard deviation and dividing it by the square root of N-th samples used to calculate the standard deviation.

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More Answers (1)

bym on 28 Aug 2011
that is correct


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