rgr (version 1.1.7)

expit: Inverse-logit transformation(s)

Description

Undertakes an inverse-logit transformation for a vector or single value.

Usage

expit(z)

Arguments

z

the value(s) to be inverse-logit transformed. Natural logarithms are used.

Value

• p
  the proportion(s) corresponding to the logit transformed value(s), z, passed to the function.

Details

Most analytical chemical data for major, minor and trace elements are of a closed form, i.e. for a sample they sum to a constant, whether it be percent, ppm (mg/kg), or some other units. It does not matter that only some components contributing to the constant sum are present in the matrix, the data are closed. As a result, as some elements increase in concentration others must decrease, this leads to statistics and graphical presentations that do not reflect the true underlying situation even in situations of univariate data analysis and display. The logit transformation provides an appropriate transformation for univariate compositional data. Procedures for removing closure effects for multivariate data are additive log-ratios (alr), centred log-ratios (clr), and isometric log-ratios (ilr).

References

Filzmoser, P., Hron, K. and Reimann, C., 2009. Univariate statistical analysis of environmental (compositional) data: Problems and possibilities. Science of the Total Environment, 407(1/3):6100-6108.

See Also

logit, alr, clr, ilr

Examples

## Generate test data
z <- c(1.6, 0, -2.3)

## Undertake and display inverse-logit transformation(s)
p <- expit(z)
p

## Clean-up
rm(z)
rm(p)