Meaning of GetErrorY, GetErrorYhigh, GetErrorYlow for TRatioPlot::GetCalculationOutputGraph

ROOT
1

Hi,
I’m using the TRatioPlot class to calculate a ratio between two histograms. I then retrieve the ratio using the TRatioPlot::GetCalculationOutputGraph function. I want to get the errors associated with the ratio, however I get different results depending on whether I use the GetErrorY, GetErrorYhigh or GetErrorYlow methods on the resulting TGraph. I can’t seem to find any information in the ROOT documentation as to how each of these differs. I calcuated the error on the ratio manually using gaussian errror propagations, and this seems to be equivalent to the output of GetErrorYlow method. However, I am at a loss as to how GetErrorY and GetErrorYhigh are calculated. Does anyone know?

ratio_errors

I’m using ROOT version 6.18/04.

Cheers,
Alex

2

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4

Hi @asopio ,
sorry for the high latency. I think we need @moneta here, let’s ping him.

Cheers,
Enrico

5

Hi,
TRatioPlot uses TGraphAsymmError::Divide with the default 'pois` option, i.e. Poisson ratio. See the reference documentation there.

Lorenzo