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From |
Reza C Daniels <rdaniels@commerce.uct.ac.za> |

To |
statalist@hsphsun2.harvard.edu |

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

Date |
Thu, 29 Sep 2005 10:09:45 +0200 |

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 * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

* * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: Generating skewed distributions on closed intervals***From:*Reza C Daniels <rdaniels@commerce.uct.ac.za>

**References**:**st: RE: Generating skewed distributions on closed intervals***From:*"Maarten Buis" <M.Buis@fsw.vu.nl>

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