plotCumulative function

Plot cumulative and category probabilities of cumulative logit model

Function for plotting cumulative and category probabilities function estimated by vglm() function from the VGAM package using the ggplot2 package.

plotCumulative(x, type = "cumulative", matching.name = "matching")

Arguments

• x: object of class vglm
• type: character: type of plot to be displayed. Options are "cumulative" (default) for cumulative probabilities and "category" for category probabilities.
• matching.name: character: name of matching criterion used for estimation in x.

Returns

An object of class ggplot and/or gg.

Examples

# loading packages
library(VGAM)

# loading data
data(Science, package = "mirt")

# total score calculation
score <- rowSums(Science)
Science[, 1] <- factor(Science[, 1], levels = sort(unique(Science[, 1])), ordered = TRUE)

# cumulative logit model for item 1
fit <- vglm(Science[, 1] ~ score, family = cumulative(reverse = TRUE, parallel = TRUE))
# coefficients for item 1
coef(fit)

plotCumulative(fit, type = "cumulative", matching.name = "Total score")
plotCumulative(fit, type = "category", matching.name = "Total score")

See Also

VGAM::vglm()

Author(s)

Tomas Jurica

Institute of Computer Science of the Czech Academy of Sciences

Adela Hladka

Institute of Computer Science of the Czech Academy of Sciences

hladka@cs.cas.cz

Patricia Martinkova

Institute of Computer Science of the Czech Academy of Sciences

martinkova@cs.cas.cz