Thanks for the reply. Naturally I already searched the site and help for the
answers to these questions. I think I've figured out how to run a
quasi-binomial model, but I cannot figure out how to test for
over-dispersion or how to apply a shapiro-wilk test.
This is not homework, neither do I have an instructor who is proficient in
using R. This program was suggested to me by another researcher after he
witnessed my frustration with the inflexibility of SPSS and other such
programs. I am on a very tight schedule and I don't have time to become a
statistician and computer scientist, which is why I wrote 3 very quick
questions asking for commands that i had already tried to find myself.
Testing for over-dispersion is probably something I can eventually get to
grips with, since I just have get variance for the real and modelled data.
However, I cannot find a command to do shapiro-wilks on the site or on these
forums. Also, why do you say that most people here wouldn't recommend this
procedure?
David Winsemius wrote:
On Nov 24, 2009, at 3:41 PM, djpren wrote:
I am looking for the correct commands to do the following things:
1. I have a binomial logistic regression model and i want to test for
overdispersion.
Under the teach a man to fish precept, ... try:
RSiteSearch(test over dispersion binomial models)
2. If I do indeed have overdispersion i need to then run a quasi-
binomial
model, but I'm not sure of the command.
?glm
# and follow the appropriate links
3. I can get the residuals of the model, but i need to then apply a
shapiro
wilk test to test them. Does anyone know the command for this?
RSiteSearch(shapiro-wilks) # not that people here recommend this
procedure
The overall flavor of these questions is homework, so I'm
speculating that you may want to consult your instructors.
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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