[ROOT] normal plots, box plots with root?

From: Isard_Dunietz (dunietz@fnal.gov)
Date: Wed Feb 28 2001 - 05:34:57 MET


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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