Sorry for the confusion. Let me put it in this way. Here we have 2000 people and we want to put them into 150 groups. The distribution of the group size follows the Gamma distribution with shape parameter 0.067 and scale parameter 0.008. At the same time, the minimum group size is 1, and the largest one should not be bigger than 85.
My questions: Can I generate a set of groups that follow the above rules by generating random draws? By the way, I also confused by the rate and scale parameters in R. I did the distribution test in SPSS and got those shape and scale parameters. In SPSS Q-Q plot, the scale parameter is 0.008. I noticed that someone mentioned that this is actually the rate. I'm confused. Thanks a lot. Garry On Tue, Nov 10, 2009 at 12:15 PM, Ravi Varadhan <rvarad...@jhmi.edu> wrote: > I think he means "rate = 0.008", so he is looking for: > > rgamma(n, shape=0.067, rate=0.008) > > Even then his problem is not well-posed. You cannot have both > "independent" > gamma rv's and have them sum to 2000. > > Ravi. > > ---------------------------------------------------------------------------- > ------- > > Ravi Varadhan, Ph.D. > > Assistant Professor, The Center on Aging and Health > > Division of Geriatric Medicine and Gerontology > > Johns Hopkins University > > Ph: (410) 502-2619 > > Fax: (410) 614-9625 > > Email: rvarad...@jhmi.edu > > Webpage: > > http://www.jhsph.edu/agingandhealth/People/Faculty_personal_pages/Varadhan.h > tml > > > > > ---------------------------------------------------------------------------- > -------- > > > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] > On > Behalf Of David Winsemius > Sent: Tuesday, November 10, 2009 2:47 PM > To: Hongwei Dong > Cc: R-help Forum; Duncan Murdoch > Subject: Re: [R] Generate Random Draw from Gamma Distribution Re: Monte > Carlo Simulation in R... > > > On Nov 10, 2009, at 2:26 PM, Hongwei Dong wrote: > > > Exactly! Thanks, Duncan. > > > > Let me re-phrase me question like this: > > > > 1) X_i values are independent Gammas, with the shape 0.067 and scale > > 0.008 > > 2) Min(X)=1 and Max(X)=85 > > You might want to check that your parameterization in in agreement > with that used by the rgamma function. Simply using those numbers > yields a distribution that does not look as though it would get many > qualifying samples. Here are 20 draws without any exclusions outside a > range: > > > rgamma(20, shape=0.067, scale = 0.008) > [1] 2.213459e-03 2.815705e-05 2.381306e-04 2.264602e-07 1.293713e-07 > 7.680773e-38 6.441082e-15 6.168961e-13 > [9] 5.089033e-06 1.571858e-16 9.869878e-12 1.813121e-13 1.253287e-11 > 1.852885e-04 4.212802e-07 1.774495e-25 > [17] 1.892984e-07 5.927422e-17 1.322638e-12 4.327472e-05 > > http://finzi.psych.upenn.edu/R/Rhelp02/archive/31459.html > > > > 3) SUM(X)=2000 > > 4) Do I also have to define the number of draws? if yes, it could be > > 250. > > > > Based on these restrictions, I want to generate random draw. I'm > > wondering > > how I can do this in R. Thanks. > > > > Garry > > > > > > > > On Tue, Nov 10, 2009 at 11:17 AM, Duncan Murdoch > > <murd...@stats.uwo.ca>wrote: > > > >> On 11/10/2009 1:25 PM, Hongwei Dong wrote: > >> > >>> Hi, Dear R users, > >>> > >>> I'm wondering if I can do Monte Carlo Simulation in R. My problem > >>> is like > >>> this: I know variable X follows Gamma distribution with shape > >>> parameter > >>> 0.067 and scale parameter 0.008. The sum of the X is 2000. I need > >>> R help > >>> me > >>> to simulate a vector of X that satisfies both the probability > >>> distribution > >>> and the sum. Anyone has a clue to this? Much appreciated. > >>> > >> > >> Your requirements are slightly contradictory or incomplete. Here's > >> one way > >> to fully specify the problem: > >> > >> The X_i values are independent Gammas, with the given shape and > >> scale. You > >> want to simulate from the joint distribution conditional on the > >> event sum(X) > >> == 2000. > >> > >> Is that your problem? I don't know how to do the simulation, but > >> maybe > >> someone else does. > >> > >> Duncan Murdoch > >> > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-help@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. > > David Winsemius, MD > Heritage Laboratories > West Hartford, CT > > ______________________________________________ > R-help@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. > > [[alternative HTML version deleted]] ______________________________________________ R-help@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.
