# Two outputs when calculating standard error of mean, WHY?

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Vlatko Milic il 7 Nov 2019
Commentato: Daniel M il 7 Nov 2019
Hi,
I am calculating the standard error of the mean and I am getting two ouput. I do not understand why. The code is:
SEM_A = std(A,[])./ sqrt(size(A))
And my output is:
SEM_A =
0.0048 0.1290
Do You have any ideas?
:)
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### Risposta accettata

Daniel M il 7 Nov 2019
Modificato: Daniel M il 7 Nov 2019
It's because size(A) returns two outputs. If you want to use the size of A in a particular dimension, use size(A,dim). (Since size operates columnwise, it's likely only dim=2 would make sense). If you want to divide by the total number of elements in A, use numel(A). If A is a vector then numel(A) is the same as length(A), which is the same as max(size(A)).
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Vlatko Milic il 7 Nov 2019
Now I think I solved it. My code is now:
STE = std(stat_W_per_K)./ sqrt(size(stat_W_per_K,2));
However, when it was:
STE = std(stat_W_per_K)./ sqrt(length(stat_W_per_K));
I got the super-low values. What is the reason for this?
Lastly, do you know how I can connect the standard error to a confidence interval of 95%? Is it my average +- my standard error and that's it? :)
Regards, Vlatko
Daniel M il 7 Nov 2019
Again it is the difference between the output of length(A) and size(A,2). I can't tell you which one is correct.
I also can't tell you how else to analyze/report your data, because I don't know what they are, how they were measured, underlying assumptions, statistical distributions, systematic errors and uncertainty, etc.

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