> On Oct 22, 2017, at 6:04 AM, Sorkin, John <jsor...@som.umaryland.edu> wrote:
>
> I have a model (run with glm) that has a factor, type. Type has two levels,
> "general" and "regional". I am trying to get estimates (and SEs) for the
> model with type="general" and type ="regional" using fit.contrast
?fit.contrast
No documentation for ‘fit.contrast’ in specified packages and libraries:
you could try ‘??fit.contrast’
Perhaps the gmodels function of that name?
> but I can't get the syntax of the coefficients to use in fit.contrast
> correct. I hope someone can show me how to use fit.contrast, or some other
> method to get estimate with SEs. (I know I can use the variance co-variance
> matrix, but I would rather not have to code the linear contrast my self from
> the coefficients of the matrix)
>
I'm having trouble understanding what you are trying to extract. There are only
2 levels so there is really only one interesting contrast ("general" vs
"regional") , and it's magnitude would be reported by just typing `model`, and
it's SE would show up in output of `summary(model)`.
I'm thinking you should pick one of the examples in gmodels::fit.contrast that
most resembles your real problem, post it, and and then explain what
difficulties you are having with interpretation.
--
David.
> Thank you,
>
> John
>
>
> My model:
>
> model=glm(events~type,family=poisson(link=log),offset=log(SS),data=data)
>
>
> Model details:
>
>> summary(data$type)
>
> general regional
> 16 16
>
>> levels(data$type)
> [1] "general" "regional"
>
>> contrasts(data$type)
> regional
> general 0
> regional 1
>
>
> I have tried the following syntax for fit.contrast
>
> fit.contrast(model,type,c(1,0))
> and get an error:
> Error in `[[<-`(`*tmp*`, varname, value = cmat) :
> no such index at level 1
>
>
>> fit.contrast(model,type,c(0,1),showall=TRUE)
> and get an error:
> Error in `[[<-`(`*tmp*`, varname, value = cmat) :
> no such index at level 1
>
>
>
>> fit.contrast(model,type,c(1,-1),showall=TRUE)
> and get an error:
> Error in `[[<-`(`*tmp*`, varname, value = cmat) :
> no such index at level 1
>
>
>> fit.contrast(model,type,c(0))
> and get an error:
> Error in make.contrasts(coeff, ncol(coeff)) :
> Too many contrasts specified. Must be less than the number of factor levels
> (columns).
>
>> fit.contrast(model,type,c(1))
> Error in make.contrasts(coeff, ncol(coeff)) :
> and get an error
> Too many contrasts specified. Must be less than the number of factor levels
> (columns).
>
>
>
>
>
>
>
>
> John David Sorkin M.D., Ph.D.
> Professor of Medicine
> Chief, Biostatistics and Informatics
> University of Maryland School of Medicine Division of Gerontology and
> Geriatric Medicine
> Baltimore VA Medical Center
> 10 North Greene Street
> GRECC (BT/18/GR)
> Baltimore, MD 21201-1524
> (Phone) 410-605-7119
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
> [[alternative HTML version deleted]]
>
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David Winsemius
Alameda, CA, USA
'Any technology distinguishable from magic is insufficiently advanced.'
-Gehm's Corollary to Clarke's Third Law
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