knitr::opts_chunk$set( collapse = TRUE, comment = "#>", fig.path = "README-", eval = FALSE )
The package permits the covariate effects of trinomial regression models to be represented graphically by means of a ternary plot. The aim of the plots is helping the interpretation of regression coefficients in terms of the effects that a change in regressors' values has on the probability distribution of the dependent variable. Such changes may involve either a single regressor, or a group of them (composite changes), and the package permits both cases to be handled in a user-friendly way. Theoretical and methodological details are illustrated and discussed in @santi2019, whereas a detailed illustration of the package and its features is available in @santi2022.
The package can read the results of both categorical and ordinal trinomial
logit regression fitted by various functions (see the next section) and
creates a field3logit
object which may be represented by means of functions
gg3logit
and stat_field3logit
.
The plot3logit
package inherits graphical classes and methods from the
package ggtern
[@hamilton2018] which, in turn, is based on the package
ggplot2
[@wickham2016a].
Graphical representation based on standard graphics is made available
through the package Ternary
[@smith2017] by functions plot3logit
and
TernaryField
, and by the plot
method of field3logit
objects.
See the help of field3logit
for representing composite effects and
multifield3logit
for drawing multiple fields and the presentation vignette
plot3logit-overview
by typing:
vignette('plot3logit-overview', package = 'plot3logit')
The paper published on Journal of Statistical Software [@santi2022] can be read as a pdf vignette by typing:
vignette('plot3logit-jss', package = 'plot3logit')
Function field3logit
of package plot3logit
can read trinomial
regression estimates from the output of the following functions:
clm
and clm2
of package ordinal
(ordinal logit regression);mlogit
of package mlogit
(logit regression);multinom
of package nnet
(logit regression);polr
of package MASS
(ordinal logit regression);vgam
and vglm
of package VGAM
(logit regression).Moreover, explicit estimates can be passed to field3logit()
. See the help of
the package (type ? 'plot3logit-package'
) and the help of functions
field3logit()
and extract3logit()
for further details.
Fit a trilogit model by means of package nnet
where the student's employment
situation is analysed with respect to all variables in the dataset
cross_1year
:
data(cross_1year) library(nnet) mod0 <- multinom(employment_sit ~ ., data = cross_1year)
The gender effect is analysed by means of a ternary plot which is generated in
two steps, however, package plot3logit
should be loaded:
library(plot3logit)
Firstly, the vector field is computed:
field0 <- field3logit(mod0, 'genderFemale')
Secondly, the field is represented on a ternary plot, using either
gg
-graphics:
gg3logit(field0) + stat_field3logit()
or standard graphics:
plot(field0)
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