#install.packages("latex2exp")
library(latex2exp)
logisticFun <- function(x,D,a,b) {
z <- D*a*(x-b)
1/(1+exp(-1*z))
}
icc <- ggplot(data.frame(x = c(-4, 4)), aes(x = x)) +
stat_function(fun = logisticFun, args = list(D=1.7,a=1,b=-.5) , colour = "red") +
stat_function(fun = logisticFun, args = list(D=1.7,a=1,b=+.5) , colour = "blue") +
scale_x_continuous(name= TeX("Ability $(\\theta)")) +
scale_y_continuous(name= TeX("$P(u=1|\\theta)"))
icc