visualize Item Information Curves.

gg_iic Calculate the item information volume from the item parameter obtained from GRM or 2PLM.

Usage

gg_iic(
  object,
  item,
  theta = c(-3, 3),
  breaks = 100,
  grm = TRUE,
  use_ltm = FALSE,
  output.data = FALSE
)

Arguments

object: mirt or grm object. If you use the grm object, you must set ltm = TRUE.
item: numeric. The number of the item to be visualized. The length must be 1.
theta: vector. The length must be 2. Specify the range of theta in the IRCCC to be visualized using c().
breaks: numeric. Specifies the number of divisions of theta. For example, if you specify 1000, the range specified by theta will be divided into 1000 parts. The default is 100.
grm: logical. The default is TRUE. If you are using a binary IRT (2PLM) object, set it to TRUE.
use_ltm: logical. The default is FALSE. If you are using an object (either an ltm object or a grm object) from the ltm package, set this to TRUE. When use_ltm = TRUE, the scale factor D is corrected to 1.701.
output.data: logical. The default is FALSE. If TRUE, instead of visualizing IRCCC, the data that forms the basis of IRCCC is output in long format.

Value

Visualize item information using ggplot2 package.

Examples

#library(mirt)
#mirt_object <- mirt(data, itemtype = "graded")

#gg_iic(mirt_object, item = 1)
#gg <- gg_iic(mirt_object, item = 1)
#gg + theme_bw()

#library(ltm)
#ltm_object <- ltm(data ~ z1, IRT.param = TRUE)

#gg_iic(ltm_object, item = 1, theta = c(-5, 5), breaks = 1000, grm = FALSE, use_ltm = TRUE)