probability.3pl: 3PL probability function

In IRTpp: Estimating IRT Parameters using the IRT Methodology

Description

The probability function in the 3PL model.

Usage

probability.3pl(z = NULL, a = z$a, b = z$b, c = NULL, d = z$d,
  cp = z$cp, theta)

Arguments

z	Optional. A list with the parameters a b and c specified by keys.
a	The discrimination parameter
b	The difficulty parameter. (Optional if d is specified)
c	The guessing parameter
d	Optional. Overrides the b parameter, it is equal to -a*b. Used in some functions.
cp	Optional. Overrides the c parameter, it is logit(c)
theta	The subject's latent trait.

Value

The value of the probability for the 3pl model.

See Also

probability.1pl, probability.2pl, prob.3pl, prob.2pl

Examples

## Simulate the test
# data <- simulateTest(model = "3PL", items = 20, individuals = 200)
## item parameters
# zita <-data$itempars
## Latent traits
# thetas <- data$latentTraits
## Probability model
# probability.3pl(zita, theta = thetas)

Example output

IRTpp documentation built on May 29, 2017, 9:58 a.m.