I am trying to make comparison of some already published data with my results. For which I need to extract data (Gaussian shaped histograms mainly). So what I do is I extract the X and Y data points from a graph and I re-plot using the method discussed in " Unable to display the histogram entries and standard deviation". When I do this I really wonder how the errors are calculated by root say, for the mean and standard deviation.

As for understanding better, I have histogram from a ttree which I am attaching below:

So i extracted the data points and I replotted the data using the method described in “Unable to display the histogram entries and standard deviation”. Please see below :

As you can see from the plots the error obatined when I replotted the data is quite different from the true error which the data has.

Can anyone tell me how to resolve this problem. How can I obtain the correct errors when I replot the data point.

Any insights about the error calculation in root would be really helpful.

Thanking you for the kind consideration!

Hi Deby,

I think your best option is to extract the errors, too, just like you extracted the X and Y values.

But the thing is not always that I have errors properly evident from the distribution. For example :

So how do I resolve this problem then?

Maybe you could contact the owners of the plot? The errors could have been set manually and do not follow any evident logic. Trying to guess the errors can be a bit unreliable.