Re: [ROOT] normal plots, box plots with root?

From: Rene Brun (Rene.Brun@cern.ch)
Date: Wed Feb 28 2001 - 17:44:13 MET


Hi Isi,

Do I understand correctly that you are proposing to implement yourself the
points 1 and 3 ? Let me know if you do it.

About your point 2, I will be happy to include the relevant piece of code if
somebody provides it.

Rene Brun

Isard_Dunietz wrote:
> 
> Dear Rene,
>    Probably the following features exist in root.  I just
> have not yet figured out  how to get at them.
> 
> 1) It is often useful to plot the data as a
> "normal quantile plot" or sometimes called a "normal plot".
> 
> Description of "normal plot" from the book by Tamhane and Dunlop,
> Statistics and Data Analysis, p. 123, is given here:
> 
> Suppose the data follow an N( mu, sigma^2 ) distribution, then the
> percentiles of that normal distribution should plot linearly against the
> sample percentiles, except for sampling variations. For the sample
> percentiles one uses normally the ordered data values themselves, the i'th
> ordered data value being the
> 100( i/(n+1)) th sample percentile, where n is the sample size.  The
> corresponding standard normal percentiles are called normal scores. The
> plot of these normal scores against the ordered data values is the normal
> plot.
> Is there some tool in root to plot out this normal plot?
> 
> 2)  It also would be useful to calculate
>     the inverse
>     cummulative density function (c.d.f.), i.e.
>     the inverse fnct of
>                 cdf( z ) = ( 1 + TMath::Erf( z / TMath::Sqrt(2) ) )
>     Is such a fnct easily obtainable inside root?
> 
> 3)  Also, is there a way to plot out data as a "box plot" or sometimes
> called a "box and whiskers plot", which plots out the following
> five important numbers
> [either bin by bin, or for each sample separately]:
> { x_min, Q_1, Q_2, Q_3, x_max }, where x_min, x_max are the
> minimum/maximum
> in the current sample and Q_k are the k'th quartile
> (25percentiles).  Please,
> see, for instance, p. 121, Tamhane and Dunlop's book.
> 
>           Thank you for your guidance.   Cheers, Isi



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