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List: r-help
Subject: Re: [R] random number generation
From: Prof Brian Ripley <ripley () stats ! ox ! ac ! uk>
Date: 2003-10-28 12:42:18
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Is this a student exercise? If not, please enlighten us as to the
real-world problem from which this is extracted.
Given that 50% of the probability mass lies between 38 and 40, and the
median and 3rd quartile are both 40, this cannot be a continuous
distribution. I would design a discrete distribution on the integers
1, ..., 99 to meet your requirements: that is `just' a constrained
non-linear optimization problem.
BTW, a random variable cannot have those characteristics: its distribution
could, or a sample could and it is unclear which you mean. The first is
easier and so that's what I have assumed.
On Wed, 29 Oct 2003, nmi13 wrote:
> I am trying to generate a random variable with the following descriptive
> statistics,
>
> min=1, max=99, variance=125, mean=38.32, 1st quartile=38, median=40, 3rd
> quartile=40, skewness=-0.274.
>
> I tried with rgamma and as I cannot use rnorm, can any one please suggest me
> what distribution would give me the negative skewness. I need to have the
> above mentioned descriptive statistics for the data generated.
>
> I would be thankful to anyone who can help me with this problem.
--
Brian D. Ripley, ripley@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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