irt_params_grm: Generate GRM Item Parameters

In irtsim: Monte Carlo Simulation-Based Sample-Size Planning for Item Response Theory

Generate GRM Item Parameters

Description

Creates a list of discrimination (a) and threshold (b) parameters suitable for passing to irt_design() with model = "GRM".

Usage

irt_params_grm(
  n_items,
  n_categories,
  a_dist = "lnorm",
  a_mean = 0,
  a_sd = 0.25,
  b_mean = 0,
  b_sd = 1,
  seed = NULL
)

Arguments

n_items	Positive integer. Number of items.
n_categories	Positive integer >= 2. Number of response categories per item. Produces n_categories - 1 threshold columns in b.
a_dist	Character string for the discrimination distribution. Currently only "lnorm" is supported. Default: "lnorm".
a_mean	Numeric. meanlog for the log-normal distribution. Default: 0.
a_sd	Numeric. sdlog for the log-normal distribution. Default: 0.25.
b_mean	Numeric. Mean around which thresholds are centered. Default: 0.
b_sd	Numeric. SD of the base threshold distribution. Default: 1.
seed	Optional integer seed for reproducibility.

Value

A named list with elements:

a

Numeric vector of length n_items.

b

Numeric matrix with n_items rows and n_categories - 1 columns. Thresholds are ordered within each row.

See Also

irt_params_2pl() for 2PL parameters, irt_design() to use the generated parameters.

Examples

# GRM parameters: 15 items, 5 response categories
params <- irt_params_grm(n_items = 15, n_categories = 5, seed = 42)

irtsim documentation built on April 24, 2026, 1:07 a.m.