cross_over: A cross over function

In jvcasill/lingStuff: Tools and Gems for Linguistics Related Research

Description

This function allows you to calculate boundary/crossover point in logistic regression models.

Usage

cross_over(mod, cont_pred, grouping_var = FALSE, int_adj, slope_adj)

Arguments

mod	A glm object
cont_pred	The continuous (x) predictor
grouping_var	(logical) Set to TRUE to include grouping var
int_adj	With grouping variable, include intercept adjustment
slope_adj	With grouping variable, include interaction (slope adjustment)

Examples

# Generate data
set.seed(1)
vot = rnorm(20, 15, 5)
vot = sort(vot)
phon1 = c(0,1,0,0,0,0,0,1,0,1,0,1,0,1,1,1,1,1,1,1)
group1 = rep('g1', 20)
df1 = data.frame(vot = vot, phon = phon1, group = group1)

phon2 = c(1,0,0,0,0,0,0,0,0,0,0,1,0,1,1,1,1,1,1,1)
group2 = rep('g2', 20)
df2 = data.frame(vot = vot, phon = phon2, group = group2)
df <- rbind(df1, df2)

# Fit model
glm1 <- glm(phon ~ vot, data = df, family = "binomial")
glm2 <- glm(phon ~ vot * group, data = df, family = "binomial")

# Get crossover point
cross_over(mod = glm1, cont_pred = 'vot')

# Get crossover point of grouping variables
cross_over(mod = glm2, cont_pred = 'vot')
cross_over(mod = glm2, cont_pred = 'vot', grouping_var = TRUE, 
           int_adj = 'groupg2', slope_adj = 'vot:groupg2')

# Plot regression with crossover point
library(ggplot2)
ggplot(df, aes(x = vot, y = phon)) + 
  geom_smooth(method = 'glm', method.args = list(family = 'binomial')) + 
  geom_vline(xintercept = cross_over(mod = glm1, cont_pred = 'vot'))

ggplot(df, aes(x = vot, y = phon, color = group)) + 
  geom_smooth(method = 'glm', method.args = list(family = 'binomial'), 
              se = FALSE) + 
  geom_vline(xintercept = cross_over(mod = glm2, cont_pred = 'vot')) +
  geom_vline(xintercept = cross_over(mod = glm2, cont_pred = 'vot', 
                                     grouping_var = TRUE, 
                                     int_adj = 'groupg2', 
                                     slope_adj = 'vot:groupg2'))

jvcasill/lingStuff documentation built on April 9, 2021, 10:42 a.m.