# Systematic error bar per bin

Hello Rooters,

I need your help to figure out this. I have two histograms as follows.

h1->Fill(variable, weight);
h1->sumW2();
h2->Fill(variable, weight_uncertainty);

What could be the total statistics + systematics error bar per bin?

= sqrt{err_weight(bin i)^2 + err_syst(bin i)^2}
or just
= err_syst(bin i)

err_weight(bin i) = error value of bin i of variable_weight
and
err_syst(bin i) = error value of bin i of variable_weight_uncertainty

thnaks
Dil

Hi @Dil ,
if I understand correctly, this is less a question about ROOT and more a question about statistics. Let’s see if @moneta has some suggestions, otherwise you should ask your research group’s statistics expert.

Cheers,
Enrico

Hi,
The total error (statistical one and the one given by the weights uncertainties) can be approximated with
`sqrt{err_weight(bin i)^2 + err_syst(bin i)^2}` using your definitions or err_weight and err_syst.

Lorenzo

Thank you Lorenzo.