See inline. -- Bert
Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Mon, Oct 3, 2016 at 3:30 PM, Paul Sanfilippo <prs...@gmail.com> wrote: > Hi, > > I am trying to replicate a test in the Hosmer - Applied Logistic regression > text (pp 289, 3rd ed) that uses a Multivariable Wald test to test the > equality of coefficients across the 2 logits of a 3 category response > multinomial model. I’d like to see whether (from a statistical standpoint) > it is acceptable to collapse the 2 response categories and then simply use a > binary logistic regression. "The idea is that if the coefficients across the 2 logits are similar (non-significant p value with Wald test), then it is reasonable to pool the categories." IMHO, this is a bad idea. See http://www.nature.com/news/statisticians-issue-warning-over-misuse-of-p-values-1.19503. Significance or lack of it is not a legitimate criterion on which to base scientific decisions. > > There does not seem to be a built in way to do this in R? > > Using the mtcars dataset as an example (for the sake of the example, using > cyl as a 3-factor response), does anyone have any ideas how to do this > > library(nnet) > data(mtcars) > mtcars$cyl <- as.factor(mtcars$cyl) > mtcars$am <- as.factor(mtcars$am) > mod <- multinom(cyl ~ am + hp, data=mtcars) > summary(mod) > >> summary(mod) > Call: > multinom(formula = cyl ~ am + hp, data = mtcars) > > Coefficients: > (Intercept) am1 hp > 6 -42.03847 -3.77398 0.4147498 > 8 -92.30944 -26.27554 0.7836576 > > So, I want to simultaneously test whether the 3 coefficients across the 2 > logits are similar. > > Thank you. > > > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.