CalculateItemDifferences {DFIT}

Calculates the differences between two item option characteristic curves for all options (minus one).

Description

Calculates the differences between two item option characteristic curves for all options (minus one).

Usage

CalculateItemDifferences(
  thetaValue,
  itemParameters,
  irtModel = "2pl",
  logistic = TRUE
)

Arguments

thetaValue

A numeric value or array for the theta (ability) value(s) for which the difference will be calculated

itemParameters

A list containing "focal" and "reference" item parameters. Item parameters are assumed to be on the same scale. Item parameters for each group should me a matrix with nrow equal to the number of items.

irtModel

A string stating the irtModel to be used. Should be one of "1pl", "2pl", "3pl", "grm" or "pcm".

logistic

A logical value stating if the IRT model will use the logistic or the normal metric.

Value

difference A numeric matrix with the differences on probabilities or on expected score for each item between focal and reference groups.

Author(s)

Victor H. Cervantes <vhcervantesb at unal.edu.co>