On Jul 6, 2012, at 4:30 PM, Abraham Mathew wrote:

Ok, so let's say I have a logit equation outlined as Y= 2.5 + 3X1 + 2.3X2 +
4X3 + 3.6X4 + 2.2X5

So a one unit increase in X2 is associated with a 2.3 increase in Y,

Assuming, that is, you also understand what Y is. From you comments so far, I have some nagging worries regarding your understanding of that point.

--
David.

regardless of what the other
predictor values are. So I guess instead of trying to plot of curve with
all the predictors accounted
for, I should plot each curve by itself.

I'm still not sure how to do that with so many predictors.

Any help would be appreciated.




On Thu, Jul 5, 2012 at 4:23 PM, Bert Gunter <gunter.ber...@gene.com> wrote:

You have an about 11-D response surface, not a curve!

-- Bert

On Thu, Jul 5, 2012 at 2:39 PM, Abraham Mathew <abmathe...@gmail.com>wrote:

I have a logit model with about 10 predictors and I am trying to plot the
probability curve for the model.

Y=1 = 1 / 1+e^-z  where  z=B0 + B1X1 + ... + BnXi

If the model had only one predictor, I know to do something like below.

mod1 = glm(factor(won) ~ as.numeric(bid), data=mydat,
family=binomial(link="logit"))

all.x <- expand.grid(won=unique(won), bid=unique(bid))
y.hat.new <- predict(mod1, newdata=all.x, type="response")

plot(bid<-000:250,predict(mod1,newdata=data.frame(bid<- c(000:250)),type="response"),
lwd=5, col="blue", type="l")


I'm not sure how to proceed when I have 10 or so predictors in the logit
model. Do I simply expand the
expand.grid() function to include all the variables?

So my question is how do I form a plot of a logit probability curve when I
have 10 predictors?

would be nice to do this in ggplot2.

Thanks!


--
*Abraham Mathew
Statistical Analyst
www.amathew.com
720-648-0108
@abmathewks*



David Winsemius, MD
West Hartford, CT

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