psychotools (version 0.7-4)

rgpcm: Simulate Data under a Generalized Partial Credit Model

Description

rgpcm simulates IRT data under a generalized partial credit model.

Usage

rgpcm(theta, a, b, nullcats = FALSE, return_setting = TRUE)

Value

rgpcm returns either a list of the following components:

a

list of numerics of item discrimination parameters used,

b

list of numeric vectors of item threshold parameters used,

theta

numeric vector of person parameters used,

data

numeric matrix containing the simulated data,

or (if return_setting = FALSE) only the numeric matrix containing the simulated data.

Arguments

theta

numeric vector of person parameters. Can also be a list, then a list of length length(theta) is returned, containing multiple simulated data sets.

a

list of numerics of item discrimination parameters.

b

list of numeric vectors of item threshold parameters.

nullcats

logical. Should null categories be allowed?

return_setting

logical. Should a list containing slots of "a", "b", and "theta", as well as the simulated data matrix "data" be returned (default) or only the simulated data matrix?

See Also

rpcm, rrsm, rpl, rrm

Examples

set.seed(1)
## item responses under a GPCM (generalized partial credit model) from
## 6 persons with three different person parameters
## 8 items with different combinations of two or three threshold parameters
## and corresponding discrimination parameters
ppar <- rep(-1:1, each = 2)
tpar <- rep(list(-2:0, -1:1, 0:1, 0:2), each = 2)
dpar <- rep(list(1, 2), each = 4)
sim <- rgpcm(theta = ppar, a = dpar, b = tpar)

## simulated item response data along with setting parameters
sim

## print and plot corresponding item response object
iresp <- itemresp(sim$data)
iresp
plot(iresp)