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Re: st: generating synthetic data with a negatively skewed distribution?


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: generating synthetic data with a negatively skewed distribution?
Date   Mon, 18 Mar 2013 18:20:26 +0000

Why the uncertainty? It is apparent from e.g.
http://en.wikipedia.org/wiki/Beta_distribution that a beta
distribution with parameters a, b will be left-skewed if b < a; thus
an example such as

. gen x = rbeta(6, 1)

generates a left-skewed distribution on [0, 1] Shift and scale to
taste. If you want a particular skewness, you need to do some
calculations first.

Nick

On Mon, Mar 18, 2013 at 6:07 PM, Gwinyai Masukume
<parturitions@gmail.com> wrote:
> many thanks Nick. In my particular case, i'm not sure how to structure
> the rbeta(a, b) argument. please kindly give an example.
> kind regards,
> gwinyai
>
> On 3/18/13, Nick Cox <njcoxstata@gmail.com> wrote:
>> If your criteria are no more than bounded support and negative skew,
>> then a beta distribution is indeed one solution.
>>
>> See -help rbeta()-.
>>
>> Nick
>>
>> On Mon, Mar 18, 2013 at 2:55 PM, Gwinyai Masukume
>> <parturitions@gmail.com> wrote:
>>
>>> I'm using version 12.1.
>>>
>>> I'd like to generate synthetic data with a ? negatively skewed
>>> distribution.
>>>
>>> gen x =3D int(1964+(1999-1964)*runiform())
>>>
>>> I would for example like a peak of events at say 1983, with more events
>>> between 1983 and 1999 (with fewer events between 1964 and 1983).
>>>
>>> I suspect that drawing from a beta distribution may work?
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