[R] Change color of plot points based on values of a variable

Richard.Cotton at hsl.gov.uk Richard.Cotton at hsl.gov.uk
Wed Oct 1 10:34:27 CEST 2008

> I have run a logistic regression, used Gelman et al.'s car package 
> to simulate the parameter estimates of that model, and have plotted 
> the probability (using Gelman et al.'s invlogit() function) of the 
> dependent variable being 1 given the value of a particular 
> independent variable is at its mean.  The plot has probabilities on 
> the y-axis and the number (1-1000) of the simulation run on the x-axis. 
> What I would like to do is to make the points that make up the 95% 
> CI a different color from the points outside that CI.  In other 
> words, I would like the points from 1-24, and 976-1000 to be one 
> color (the default color is fine), and the points 25-975 to be a 
> different color. How would I do this?
> In case there is some confusion, here is example code, with only 
> set.seed(23)
> y<-rbinom(100,1,0.1)
> x<-rnorm(100)
> fit.1<-glm(y~x1, family=binomial(link="logit"))
> library(car)
> sim.fit.1<-sim(fit.1, 1000)   #Simulate the parameter estimates of 
> fit.1 1000 times
> plot(sort(invlogit(sim.fit.1$beta[,1]+sim.fit.2$beta[,2]*mean(x1))))

Running your code throws an error for me (can't find the 'sim' function - 
is it in another library?).  I think this is what you are trying to 
achieve though

plot(1:20, col=c(rep("red",5), rep("blue",10), rep("red",5)))


Mathematical Sciences Unit


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