[R] Creating a specific skewed distribution

[Etienne B. Racine]

You could also make some algebra. e.g. :

?rweibull

gives the formula of the mean and of the cumulative distribution function in
the Details section. So using your known parameters (i.e. mean=30 and
p(10)=.10, i.e. cumulative function(10) =.90), I think it is sufficient to
determine the exact values you want shape and scale to be.

And you can do that with any probability function (some easier the
calculate) as most (if not all) have these equations. Of course, it might be
more pleasing to play with the parameters.

Etienne


Mike Lawrence wrote:
> 
> With skewed unimodal distributions, the mode can't equal the mean, so
> assuming you want the mean to be around 30, I find that a weibull
> function can get close to what you want:
> 
>> mean(rweibull(1e5,1.5,33))
> [1] 29.77781
>> pweibull(60,1.5,33)
> [1] 0.9138475
> 
> I'm sure you can play with the parameters to try to get even closer to
> what you want.
> 
> On Wed, Jun 10, 2009 at 2:48 AM, David Arnold<dwarnold45 at suddenlink.net>
> wrote:
>> All,
>> Can someone help me create a skewed distribution, mean = 30, with
>> probability of selecting a random number from the distribution greater
>> than or equal 60 equal to 10%?
>>
>> I need the probability density function to equal zero at zero, and
>> have  a maximum height at or near 30.
>>
>> Is this possible?
>>
>> And if it is possible, how can I adjust the distribution so that the
>> probability of selecting a random number greater than or equal to 60
>> is p.
>>
>> Thanks. No idea how to start.
>>
>> David
>>
>>
>>
>>        [[alternative HTML version deleted]]
>>
>> ______________________________________________
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>> and provide commented, minimal, self-contained, reproducible code.
>>
> 
> 
> 
> -- 
> Mike Lawrence
> Graduate Student
> Department of Psychology
> Dalhousie University
> 
> Looking to arrange a meeting? Check my public calendar:
> http://tr.im/mikes_public_calendar
> 
> ~ Certainty is folly... I think. ~
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 

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