Re: Histogram mean

Stefan and Aammer:

What would be nice would be an option, e.g., GetMean("binned") vs. GetMean("unbinned") with default being what folks are used to.

I suspect that problem occurs not just for subtracted historgrams but for weighted ones.

On the other hand sometimes you want the unbinned mean. If you've made big bins to make the plot look nice, the mean may be seriously over estimated by using middle of the bin ...

Maybe there should be a warning when |h->Sumw2()| has been involked ...

-Art S.

A.E. Snyder, The Former Group C (TFC)        \!c*p?/
SLAC Mail Stop #95                          ((.   .))
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                                                 &
                                            Fermi/GLAST

On Tue, 13 Sep 2011, Stefan Piperov wrote:

>
> This issue - that ROOT reports histogram's momenta based on unbinned
> data - has been discussed several times now, but without much
> consequences...
>
> It is plain wrong, of course, to report quantities related to the
> initial dataset as belonging to the histogram, but this is how ROOT was
> designed from the very beginning, so it's too late now to change, I
> guess. What we can do, though, is to spread the word, so that at least
> the users know of this problem, and do not rely on TH1::GetMean() to get
> the mean of the binned data.
>
> Stefan.
>
>
> On Tue, 13 Sep 2011, Arthur E. Snyder wrote:
>
>> Aamer,
>>
>> It doesn't work on subtracted histograms. I had to 'roll-my-own' to do that
>> (though there might be something existing that does this that I just didn't
>> find).
>>
>> As I recall |root] does unbinned mean, so you get the same result regardless
>> of binning. It's not clear what it does the case of subtracted histograms,
>> but if the histograms is asymmetric the result can be wildly wrong.
>>
>> -Art S.
>>
>> A.E. Snyder, The Former Group C (TFC) \!c*p?/
>> SLAC Mail Stop #95 ((. .))
>> Box 4349 |
>> Stanford, Ca, USA, 94309 '\|/`
>> e-mail:snyder_at_slac.stanford.edu o
>> phone:650-926-2701 _
>> http://www.slac.stanford.edu/~snyder BaBar
>> FAX:707-313-0250 Collaboration
>> &
>> Fermi/GLAST
>>
>>
>>
>> On Tue, 13 Sep 2011, Aamer Wali Rauf wrote:
>>
>>> Hi,
>>> I have always assumed (and thus used) that the TH1::GetMean(1) method gives
>>> out the weighted mean value
>>> of the x-axis of the histogram. Visibly it looks to me that way but is it
>>> really so? Can someone
>>> comment on that please?
>>>
>>> Thanks in advance,
>>> Aamer
>>>
>>>
>>
>
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Received on Tue Sep 13 2011 - 22:16:18 CEST