Re: [R] Strange error with log-normal models

2013-04-16 Thread Ben Bolker
peter dalgaard gmail.com> writes: > On Apr 16, 2013, at 22:20 , Noah Silverman wrote: > > > My challenge here is finding the right model for this data. > Originally it was a nice count of students. Relatively easy to > model with a zero inflated Poisson model. The resulting residuals > seeme

Re: [R] Strange error with log-normal models

2013-04-16 Thread peter dalgaard
On Apr 16, 2013, at 22:20 , Noah Silverman wrote: > @Duncan, You make a very good point. Somehow I overlooked that 0 is not > positive. I guess that rules out the log normal model. > > My challenge here is finding the right model for this data. Originally it > was a nice count of students.

Re: [R] Strange error with log-normal models

2013-04-16 Thread Marc Schwartz
Noah, You might want to look at beta regression, using the betareg package on CRAN. There is a JSS paper here that you might find helpful: http://www.jstatsoft.org/v34/i02/paper along with the vignettes for the package: http://cran.r-project.org/web/packages/betareg/vignettes/betareg.pdf

Re: [R] Strange error with log-normal models

2013-04-16 Thread Noah Silverman
@Duncan, You make a very good point. Somehow I overlooked that 0 is not positive. I guess that rules out the log normal model. My challenge here is finding the right model for this data. Originally it was a nice count of students. Relatively easy to model with a zero inflated Poisson model

Re: [R] Strange error with log-normal models

2013-04-16 Thread Thomas Lumley
On Wed, Apr 17, 2013 at 5:19 AM, Noah Silverman wrote: > Hi, > > I have some data, that when plotted looks very close to a log-normal > distribution. My goal is to build a regression model to test how this > variable responds to several independent variables. > [snip] When I try to build a sim

Re: [R] Strange error with log-normal models

2013-04-16 Thread Duncan Murdoch
On 16/04/2013 1:19 PM, Noah Silverman wrote: Hi, I have some data, that when plotted looks very close to a log-normal distribution. My goal is to build a regression model to test how this variable responds to several independent variables. To do this, I want to use the fitdistr tool from the

[R] Strange error with log-normal models

2013-04-16 Thread Noah Silverman
Hi, I have some data, that when plotted looks very close to a log-normal distribution. My goal is to build a regression model to test how this variable responds to several independent variables. To do this, I want to use the fitdistr tool from the MASS package to see how well my data fits t