```
# NOT RUN {
curve(logistic(x,a=1.702),-3,3,ylab="Probability of x",
main="Logistic transform of x",xlab="z score units")
#logistic with a=1.702 is almost the same as pnorm
curve(pnorm(x),add=TRUE,lty="dashed")
curve(logistic(x),add=TRUE)
text(2,.8, expression(alpha ==1))
text(2,1.0,expression(alpha==1.7))
curve(logistic(x),-4,4,ylab="Probability of x",
main = "Logistic transform of x in logit units",xlab="logits")
curve(logistic(x,d=-1),add=TRUE)
curve(logistic(x,d=1),add=TRUE)
curve(logistic(x,c=.2),add=TRUE,lty="dashed")
text(1.3,.5,"d=1")
text(.3,.5,"d=0")
text(-1.5,.5,"d=-1")
text(-3,.3,"c=.2")
#demo of graded response model
curve(logistic.grm(x,r=1),-4,4,ylim=c(0,1),main="Five level response scale",
ylab="Probability of endorsement",xlab="Latent attribute on logit scale")
curve(logistic.grm(x,r=2),add=TRUE)
curve(logistic.grm(x,r=3),add=TRUE)
curve(logistic.grm(x,r=4),add=TRUE)
curve(logistic.grm(x,r=5),add=TRUE)
text(-2.,.5,1)
text(-1.,.4,2)
text(0,.4,3)
text(1.,.4,4)
text(2.,.4,5)
# }
```

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