Re: st: RE: Generating skewed distributions on closed intervals

[Reza C Daniels <rdaniels@commerce.uct.ac.za>]

Hi again, again!

I've found a solution to the uniform distribution in the -egen var=seq() 
from() to()- command.

Is it not simpler just to try and transform this into the three 
appropriate normal and skewed distributions than to use the -betaden- 
set of commands? If so, how? If not, I revert to below.

Thanks again,
Reza




Reza C Daniels wrote:

> Hi again,
>
> I'm not sure I'm getting the intuition behind the code of the beta 
> density functions -betaden- and -nbetaden-. My reading suggests using 
> -betaden- for the symmetric ~ about 25, and -nbetaden- for the skewed ~s 
> about 22.5 & 27.5.
>
> However, when I plug in the numbers I get a single result. Clearly I'm 
> doing something very wrong. Does this mean I need to calculate a & b & 
> lambda (shape paramaters in betaden commands) first somehow?
>
> Thanks,
> Reza
>
>
> Maarten Buis wrote:
>
>
> > you can have a look at the beta distribution
> > a normal distribution will never stay within an interval (except 
> > [minus infinity, plus infinity])
> >
> >
> > -----Original Message-----
> > From: owner-statalist@hsphsun2.harvard.edu 
> > [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Reza C Daniels
> > Sent: donderdag 29 september 2005 9:25
> > To: statalist@hsphsun2.harvard.edu
> > Subject: st: Generating skewed distributions on closed intervals
> >
> > Dear Statalisters
> >
> > I have a categorical variable for agegroup in 10 year bands (e.g. 20-30
> > years old). I would like to convert the categorical age variable to a
> > continuous variable by imposing various distributions on the range of
> > each interval. I then want to conduct sensitivity analysis to my
> > distributional assumptions.
> >
> > For example: let a = the lower limit and b = upper limit for each age
> > group (e.g. a= 20 years old, b= 30 years old). Keeping the [20,30]
> > example, the four distributions I want to examine are:
> >
> > 1) Uniformly distributed over [20,30].
> > 2) Normally distributed on the closed interval [20,30], with mode at 25.
> > 3) Positively skewed on the closed interval [20,30], with mode at 22.5.
> > 4) Negatively skewed on the closed interval [20,30], with mode at 27.5.
> >
> > I have tried various commands (including -drawnorm-), but am unable to
> > control my variance to ensure the tails are bounded by [20,30] in the
> > example above (generically, the interval [a,b]).
> >
> > Any suggestions on the code for all four distributions above would be
> > very much appreciated.
> >
> > With thanks,
> > Reza
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