car (version 2.1-4)

logit: Logit Transformation

Description

Compute the logit transformation of proportions or percentages.

Usage

logit(p, percents=range.p[2] > 1, adjust)

Arguments

p

numeric vector or array of proportions or percentages.

percents

TRUE for percentages.

adjust

adjustment factor to avoid proportions of 0 or 1; defaults to 0 if there are no such proportions in the data, and to .025 if there are.

Value

a numeric vector or array of the same shape and size as p.

Details

Computes the logit transformation logit \(=\log [p/(1-p)]\) for the proportion \(p\).

If \(p=0\) or \(1\), then the logit is undefined. logit can remap the proportions to the interval (adjust, 1 - adjust) prior to the transformation. If it adjusts the data automatically, logit will print a warning message.

References

Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.

See Also

probabilityAxis

Examples

options(digits=4)
logit(.1*0:10)
##  [1] -3.6636 -1.9924 -1.2950 -0.8001 -0.3847  0.0000  0.3847
##  [8]  0.8001  1.2950  1.9924  3.6636
## Warning message: 
## proportions remapped to (0.025, 0.975) in: logit(0.1 * 0:10) 

logit(.1*0:10, adjust=0)
##  [1]    -Inf -2.1972 -1.3863 -0.8473 -0.4055  0.0000  0.4055
##  [8]  0.8473  1.3863  2.1972     Inf