Calculate 2 standard deviations

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));

Answer 1

[Wayne King]

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

[jay yawson]

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

[Thomas To]

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.

Answer 2

[bym]

that is correct