[R] logistic regression
Mike Lawrence
Mike.Lawrence at DAL.CA
Thu Jul 26 15:06:59 CEST 2007
Maybe try making sure the data is numeric:
fac.to.num=function(x) as.numeric(as.character(x))
On 26-Jul-07, at 9:34 AM, Sullivan, Mary M wrote:
> Greetings,
>
>
> I am working on a logistic regression model in R and I am
> struggling with the code, as it is a relatively new program for
> me. In searching Google for 'logistic regression diagnostics' I
> came Elizabeth Brown's Lecture 14 from her Winter 2004
> Biostatistics 515 course (http://courses.washington.edu/b515/
> l14.pdf) . I found most of the code to be very helpful, but I am
> struggling with the lines on to calculate the observed and expected
> values in the 10 groups created by the cut function. I get error
> messages in trying to create the E and O matrices: R won't accept
> assignment of "fi1c==j" and it won't calculate the sum.
>
>
>
> I am wondering whether someone might be able to offer me some
> assistance...my search of the archives was not fruitful.
>
>
>
> Here is the code that I adapted from the lecture notes:
>
>
>
> fit <- fitted(glm.lyme)
>
> fitc <- cut(fit, br = c(0, quantile(fit, p = seq(.1, .9, .1)),1))
>
> t<-table(fitc)
>
> fitc <- cut(fit, br = c(0, quantile(fit, p = seq(.1, .9, .1)), 1),
> labels = F)
>
> t<-table(fitc)
>
>
>
> #Calculate observed and expected values in ea group
>
> E <- matrix(0, nrow=10, ncol = 2)
>
> O <- matrix(0, nrow=10, ncol=2)
>
> for (j in 1:10) {
>
> E[j, 2] = sum(fit[fitc==j])
>
> E[j, 1] = sum((1- fit)[fitc==j])
>
> O[j, 2] = sum(pcdata$lymdis[fitc==j])
>
> O[j, 1] = sum((1-pcdata$lymdis)[fitc==j])
>
>
>
> }
>
>
>
> Here is the error message: Error in Summary.factor(..., na.rm =
> na.rm) :
> sum not meaningful for factors
>
>
>
>
>
> I understand what it means; I just can't figure out how to get
> around it or how to get the output printed in table form. Thank
> you in advance for any assistance.
>
>
>
> Mary Sullivan
>
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--
Mike Lawrence
Graduate Student, Department of Psychology, Dalhousie University
Website: http://memetic.ca
Public calendar: http://icalx.com/public/informavore/Public
"The road to wisdom? Well, it's plain and simple to express:
Err and err and err again, but less and less and less."
- Piet Hein
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