Calculate 2 standard deviations
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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));
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Accepted Answer
Wayne King
on 28 Aug 2011
Hi Chris, for a matrix of data
x = randn(10,4);
mean(x)+2*std(x)
mean(x)-2*std(x)
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.
Wayne
2 Comments
jay yawson
on 17 Jun 2019
Hello Wayne King. In this case, how would you calculate the standard error of the mean?
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. ![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/262737/image.png)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/262737/image.png)
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