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st: Overlaid curves


From   absc11@bangor.ac.uk
To   statalist@hsphsun2.harvard.edu
Subject   st: Overlaid curves
Date   Sun, 21 Mar 2004 03:21:01 +0000

Dear Statalisters,

I have a dataset that is potentially contaminated by samples from more than one
population (implications from bimodality). 

I need to graph the histogram (or maybe the kernel) of the unified sample and on
the same time to overlay three more curves.
(1)The -normal- curve that exists in the options of -hist- or -kdensity-;
(2)Another bell-shaped curve:, e.g. Normal(mean=-.01,sd=2) or
Logistic(a=-.01,b=2);
(3)And a positively distrituted curve, e.g. Generalised
Beta(a1=0.01,a2=2,min=0,max=1) or Lognormal(mean=0.01,sd=2).

The particularity of my sample is that it takes values only in the [-1,1]
interval. I realise that the normal or the student distribution are not the
best fitts for such a sample, but the case of the  Beta seems to be a good
solution for one of the curves (positively distributed) that I wish to
overlay.
The personalised bell-shaped curve is to exhibit (manualy) the existence of
another mode in the distribution and I dont mind if the tails go further than
the [-1,1] interval. However, it would be nice if I could fit Pearson-Type of
curves with finite-limits.

I would like to know how can I overlay the separate curves with the personalised
parameters, and also if there is a 'library' of supported distributions in
Stata.

many thanks in advance,
Dimitris



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