Kolmogorov and chi2 test in ROOT

ROOT
1

Hello,

I am an ATLAS physicist, working on physics analysis.

I have been asked to test the compatibility between two histograms with a Kolmogorov-Smirnov and chi2 tests.

I have implemented in ROOT this using TH1 default functions:

    KS = histo_1.KolmogorovTest(histo_2)
    chi2 = histo_1.Chi2Test(histo_2)

and I am getting the numerical results which you see in the plot caption:

Screenshot 2025-04-15 at 13.47.32
Screenshot 2025-04-15 at 13.47.321630×1382 170 KB

Can some expert help me in interpreting the thresholds? If I want to test the compatibility of the two hitsograms at 95%, what threshold I have to check in the KS and chi2 test?

Thanks a lot,
Giovanni Padovano (ATLAS)

2

Hello, if someone with expertise can help with this it is very much appreciated

3

Hi Giovanni,

Let me add @moneta in the loop. Please mind that during this period answers can be a bit delayed due to various holidays.

D