[R] Fitting gamma and exponential Distributions with fitdist

[Joshua Wiley]

Hi,

I am not incredibly knowledgeable about gamma distributions, but
looking at your data, you have a tiny mean:variance ratio, which, I
believe, means that the bulk of the distribution will be near 0 and
you may run into computational problems (again I think.  I would
gladly be corrected).  This all makes me think it might be a
convergence issue.  Perhaps you can transform your data for estimation
and then transform it back (not sure if this would yield equivalent
results)?

fitdist(test + 10^4, "gamma")
fitdist(test/10^4, "gamma")

Good luck,

Josh


On Wed, Apr 27, 2011 at 9:42 PM, vioravis <vioravis at gmail.com> wrote:
> There was a small error in the data creation step and have fixed it as below:
>
> test <- c(895.1358,2915.7447,335.5472,1470.4022,194.5461,1814.2328,
> 1056.3067,3110.0783,11441.8656,142.1714,2136.0964,1958.9022,
> 891.89,352.6939,1341.7042,167.4883,2502.0528,1742.1306,
> 837.1481,867.8533,3590.4308,1125.9889,1200.605,4321.0011,
> 1873.9706,323.6633,1912.3147,865.6058,2870.8592,236.7214,
> 580.2861,350.9269,6842.4969,1886.2403,265.5094,199.9825,
> 1215.6197,7241.8075,2381.9517,3078.1331,5461.3703,2051.3997,
> 751.6575,714.3536,598.4539,425.6656,215.2103,608.785,
> 369.4744,2398.6506,918.6844,525.6925,2549.3694,4108.8983,
> 2824.0758,1068.7508,249.995,3863.9839,1152.1506,531.6844)
>
> Any help would be appreciated. Thank you.
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Fitting-gamma-and-exponential-Distributions-with-fitdist-tp3477391p3480133.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.
>



-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/