Calculates the differences between two item option characteristic curves for all options (minus one).
CalculateItemDifferences(
thetaValue,
itemParameters,
irtModel = "2pl",
logistic = TRUE
)A numeric value or array for the theta (ability) value(s) for which the difference will be calculated
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.
A string stating the irtModel to be used. Should be one of "1pl", "2pl", "3pl", "grm" or "pcm".
A logical value stating if the IRT model will use the logistic or the normal metric.
difference A numeric matrix with the differences on probabilities or on expected score for each item between focal and reference groups.