[R] Strange error with log-normal models

[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 the actual distribution, and also build a generalized linear model using the glm command.


The summary of my data is:  

   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
 0.0000  0.0000  0.0000  0.8617  0.8332 55.5600 

So, no missing values, no negative values.

When I try to use the fitdistr command, I get an error that I don't understand:
m <- fitdistr(y, densfun="lognormal")

Error in fitdistr(y, densfun = "lognormal") :  need positive values to fit a log-Normal



When I try to build a simple model, I also get an error:

l <- glm(y~ x, family=gaussian(link="log"))

Error in eval(expr, envir, enclos) :  cannot find valid starting values: please specify some



Can anyone offer some suggestions?


Thanks!

--
Noah Silverman, M.S.
UCLA Department of Statistics
8117 Math Sciences Building
Los Angeles, CA 90095