What are the errors in TProfile?

ROOT
1

Hello,
If from a TH2F histogram we make a TProfile using TH2F::ProfileX() I thought that for each value of the bins in X the TProfile gives its mean Y value (the points in the TProfile) and its RMS (the vertical error bars in TProfile).
I have attached the file Histo2D.root. There are two plots inside:
TotalEclusVsE, which is a TH2F histogram and TotalEclusVsE_pfx which is a TProfile calculated from the first one doing:
TotalEclusVsE->ProfileX();

If we plot both plots together:
TotalEclusVsE->Draw();
TotalEclusVsE_pfx->Draw(“same”);

Clearly the points in TotalEclusVsE_pfx are the mean of Y for each bin, but the errors are too small to be the RMS.
What are they? The error on the mean?

I would like to have the real RMS as the error bars in TProfile to have an idea on how the Y values are spread around the mean .

Cheers.
Histo2D.root (19.5 KB)

2

Hi,

the default is t he error on the mean, RMS/sqrt(N).
However you can use RMS as error by using option “S” in the profile constructor.
See root.cern.ch/root/htmldoc/TProfi … ildOptions

Cheers

Lorenzo

3

True!

Thank you!

4

[quote=“moneta”]Hi,

the default is t he error on the mean, RMS/sqrt(N).
However you can use RMS as error by using option “S” in the profile constructor.
See root.cern.ch/root/htmldoc/TProfi … ildOptions

Cheers

Lorenzo[/quote]

I have a question concerning the RMS: Is it also possible to draw the asymmetric RMS? (RMS computed in each direction from the mean?)

5

You cannot draw asymmetric error for a TProfile.
You need to create an TGraphAsymmErrors and set yourself values and errors.

Regards

Lorenzo