Calculate 2 standard deviations

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Chris 2011-8-28

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https://ww2.mathworks.cn/matlabcentral/answers/14678-calculate-2-standard-deviations

评论： Thomas To 2020-1-20

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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Answer 1

Wayne King 2011-8-28

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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

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jay yawson 2019-6-17

Hello Wayne King. In this case, how would you calculate the standard error of the mean?

Thomas To 2020-1-20

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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