Message-ID: <200812041734.mB4HYrf2027362@hypatia.math.ethz.ch>
Date: 2008-12-04T17:34:26Z
From: Gerard M. Keogh
Subject: Simulating underdispersed counts
In-Reply-To: <B37C0A15B8FB3C468B5BC7EBC7DA14CC61C2F3E378@LP-EXMBVS10.CO.IHC.COM>
V interesting point Greg.
But are you not just suggesting left and right truncation?
It strikes me that if the data are Poission then a mixture is likely to be
better - something akin to zero-deflated.
Neg binomail works for greater variance == mix a gamma and poisson, but I'm
unsure what to mix to deflate the variance - maybe bernoulli.
In any event, one possibility is that the data are dependnent (e.g. family
data) so to get a underdispersion you could draw from the poisson and then
redraw from the result based on some condition such as closeness (e.g. as a
proxy for family size).
Hope this helps!
Gerard
Greg Snow
<Greg.Snow at imail.
org> To
Sent by: Ren? Holst <rho at aqua.dtu.dk>,
r-help-bounces at r- "R-help at r-project.org"
project.org <R-help at r-project.org>
cc
04/12/2008 17:21 Subject
Re: [R] Simulating underdispersed
counts
Accurate probably depends on what exactly you want to accomplish with the
simulation, but one simple approach would be to generate more data than you
need from a regular Poisson distribution, then throw away the extreme
values on both sides.
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111
> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Ren? Holst
> Sent: Thursday, December 04, 2008 6:40 AM
> To: R-help at r-project.org
> Subject: [R] Simulating underdispersed counts
>
> Hello,
>
> Anyone who knows a fast and accurate algorithm for generating draws
> from an underdispersed Poisson distribution. Or even better, if there
> is a package containing such an implementation.
>
> Thanks
>
> Rene
>
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> PLEASE do read the posting guide http://www.R-project.org/posting-
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> and provide commented, minimal, self-contained, reproducible code.
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