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

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?


I’m using ROOT version 6.18/04.


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


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