The nice thing about the uniform density is that it's easy to know what the expected pdf(pmf) should look like, namely each observation should have probability 1/n. That means you can use "qqplot." See ?qqplot
Here's an example, using "my.data." my.data <- runif(100) n.points <- length(my.data) expected.cdf <- ((1:n.points)-0.5)/(n.points) qqplot(my.data, expected.cdf, las=1) # Use the "interocular trauma test" for goodness-of-fit: my.lm <- lm(expected.cdf ~ sort(my.data)) abline(coef=coef(my.lm), lty=2) Charles Annis, P.E. [EMAIL PROTECTED] phone: 561-352-9699 eFax: 614-455-3265 http://www.StatisticalEngineering.com -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Amit Kabiri Sent: Saturday, December 03, 2005 11:43 AM To: 'Elizabeth Lawson'; 'David Zhao' Cc: [email protected] Subject: Re: [R] Goodness fit test HELP! If I have a Uniform distribution to check, How can I use visual fits? Can I also use in some way the qqnorm? Thanks -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Elizabeth Lawson Sent: Friday, November 18, 2005 8:06 PM To: David Zhao Cc: [email protected] Subject: Re: [R] Goodness fit test HELP! What about trying a qqplot to see how the distribution fits... For the normal distribution thta is very stright forward, use qqnorm. To test gamma distribtution (or any other) do some thing like this n<-length(data) for(i in 1:n){ prob<-(i-1/3)/(n1/3) } quantiles<-qgamma(prob,shape=mean(data)/var(data),scale=var(data)/mean(data) } qqplot(data,quantiles) If the distribution is a good for, you should a stright line, like wiht a qqnorm plot! Good luck!! Elizbaeth Lawson David Zhao <[EMAIL PROTECTED]> wrote: Hi there, I'm a newbie, plesae bear with me. I have a dataset with about 10000 ~ 30000 data points. Would like fit to both Gamma and Normal distribution to see which one fits better. How do I do this in R? Or I could do a normality test of the data, if it's normal, I then will do a normal fit, otherwise, a gamma fit. But again, I don't know how to do this either. Please help! David [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html --------------------------------- [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
