[R] Using the effects package to plot logit probabilities

[John Fox]

Dear Abraham,

It's not entirely clear to me what you want to plot. If you want the "effect
display" for each predictor holding the others to typical values,
plot(allEffects(md1)) will do that. 

But you appear to want to plot fitted probabilities for combinations of the
predictors even though the model is additive. If that's really what you
want, you should be able to get it by specifying
plot(effect("income*age*home", md1). This will generate a warning because
"income:age:home" isn't a high-order term in the model, but it should work.

I hope this helps,
 John

-------------------------------------------------------
John Fox
Senator William McMaster Professor of Social Statistics
Department of Sociology
McMaster Univeristy
Hamilton, Ontario, Canada



> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Abraham Mathew
> Sent: August-13-12 12:40 PM
> To: r-help at r-project.org
> Subject: [R] Using the effects package to plot logit probabilities
> 
> I'm trying to run a logit model and plot the probability curve for a
number of
> the important predictors. I'm trying to do this with the Effects package.
> 
> 
> df=data.frame(income=c(5,5,3,3,6,5),
>               won=c(0,0,1,1,1,0),
>               age=c(18,18,23,50,19,39),
>               home=c(0,0,1,0,0,1))
> str(df)
> 
> md1 = glm(factor(won) ~ income + age + home,
>           data=df, family=binomial(link="logit"))
> 
> summary(md1)
> 
> plot(effect("income", md1), grid=TRUE)
> 
> 
> But I want to know how to plot a graph so that it shows the probability of
> won (response) based on income (or any of the other predictors).
> 
> However, what I want to do is generate the same plot, with won don y axis
> and income on x axis, but the curves showing the probabilities for age and
> home.
> 
> 
> Not seeing how to do this in the effects documentation. Help!
> 
> 
> Thanks.
> 
> 
> 
> --
> *Abraham Mathew
> Statistical Analyst
> www.amathew.com
> 720-648-0108
> @abmathewks*
> 
> 	[[alternative HTML version deleted]]
> 
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