Dear All,
Can any one explain the meaning of the function GetEffectiveEntries();
In the documentation “http://root.cern.ch/root/html/TH1.html#TH1:GetEffectiveEntries” it is written like
" number of effective entries of the histogram" .
My question is whether it implies the total no. of bins or the summation of entries in each bin.
Regards-
Kalyan
Hi,
The number of effective entries is defined as : (Sum of weights )^2 / (Sum of weight^2 )
where the sum is considered on all histogram bins.
In case of an unweighted histogram this number is then equivalent to the number of entries of the histogram.
For a weighted histogram, this number corresponds to the hypotetical number of unweighted entries
a histogram would need to have the same statistical power.
The documentation is maybe not very clear. I will update it
Best Regards
Lorenzo