logit function

Logit Transformation

Compute the logit transformation of proportions or percentages.

logit(p, percents, adjust)

Arguments

• p: numeric vector or array of proportions or percentages.
• percents: TRUE for percentages, FALSE for proportions. If the argument is missing and the largest value of p > 1, percents is set to TRUE, otherwise to FALSE.
• 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.

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.

Returns

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

References

Fox, J. and Weisberg, S. (2019) An R Companion to Applied Regression, Third Edition, Sage.

Author(s)

John Fox jfox@mcmaster.ca

See Also

probabilityAxis

Examples

save.opt <- options(digits=4)
logit(.1*0:10)
logit(.1*0:10, adjust=0)
options(save.opt)