R: Logistic and Inverse logistic functions

invlogit {arm} | R Documentation

## Logistic and Inverse logistic functions

### Description

Inverse-logit function, transforms continuous values to the range (0, 1)

### Usage

    logit(x)
    invlogit(x)

### Arguments

`x` | A vector of continuous values

### Details

The Inverse-logit function defined as: logit^-1(x) = e^x/(1+e^x) transforms continuous values to the range (0, 1), which is necessary, since probabilities must be between 0 and 1 and maps from the linear predictor to the probabilities

### Value

A vector of estimated probabilities

### Author(s)

Andrew Gelman gelman@stat.columbia.edu, M.Grazia Pittau grazia@stat.columbia.edu

### References

Andrew Gelman and Jennifer Hill. (2006). Data Analysis Using Regression and Multilevel/Hierarchical Models. Cambridge University Press.

### Examples

     data(frisk)
     n <- 100
     x1 <- rnorm (n)
     x2 <- rbinom (n, 1, .5)
     b0 <- 1
     b1 <- 1.5
     b2 <- 2
     Inv.logit <- invlogit(b0+b1*x1+b2*x2)
     plot(b0+b1*x1+b2*x2, Inv.logit)

[Package arm version 1.9-3 Index]