Description Usage Arguments Value Author(s) References Examples
Calculates CDIF index for an item with given item parameters of focal and reference groups.
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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". |
focalAbilities |
If NULL, NCDIF is calculated by numerical integration of focal distribution. If not NULL, it must be a numerical vector containing the abilities for the individuals in the focal group. |
focalDistribution |
A string stating the distribution name to be used for integrating. Only used if focalAbilities is NULL. |
subdivisions |
A numeric value indicating the number of subdivisions for numerical integration. Only used if focalAbilities is NULL. |
logistic |
A logical value stating if the IRT model will use the logistic or the normal metric. Defaults to using the logistic metric by fixing the D constant to 1. If FALSE the constant is set to 1.702 so that the normal metric is used. |
focalDistrExtra |
Extra parameters for the focal group distribution function if needed. |
cdif Numeric vector with the CDIF index value for each item.
Victor H. Cervantes <vhcervantesb at unal.edu.co>
Raju, N. S., van der Linden, W. J., & Fleer, P. F. (1995). IRT-based internal measures of differential functioning of items and tests. Applied Psychological Measurement, 19, 353–368. doi:10.1177/014662169501900405
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | # # Not run
# #
# # data(dichotomousItemParameters)
# #
# # threePlParameters <- dichotomousItemParameters
# # isNot3Pl <- ((dichotomousItemParameters[['focal']][, 3] == 0) |
# # (dichotomousItemParameters[['reference']][, 3] == 0))
# #
# # threePlParameters[['focal']] <- threePlParameters[['focal']][!isNot3Pl, ]
# # threePlParameters[['reference']] <- threePlParameters[['reference']][!isNot3Pl, ]
# # threePlParameters[['focal']][, 3] <- threePlParameters[['focal']][, 3] + 0.1
# # threePlParameters[['reference']][, 3] <- threePlParameters[['reference']][, 3] + 0.1
# # threePlParameters[['focal']][, 2] <- threePlParameters[['focal']][, 2] + 1.5
# # threePlParameters[['reference']][, 2] <- threePlParameters[['reference']][, 2] + 1.5
# # threePlParameters[['focal']] <- threePlParameters[['focal']][-c(12, 16, 28), ]
# # threePlParameters[['reference']] <- threePlParameters[['reference']][-c(12, 16, 28), ]
# #
# # threePlCdif <- Cdif(itemParameters = dichotomousItemParameters, irtModel = '3pl',
# # focalAbilities = NULL, focalDistribution = "norm",
# # subdivisions = 5000, logistic = TRUE)
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