Gpoly(matrix, Ncat,
NA.method = "NPModel", Save.MatImp = FALSE,
IP = NULL, IRT.PModel = "GRM", Ability = NULL, Ability.PModel = "EAP")Gnormed.poly(matrix, Ncat,
NA.method = "NPModel", Save.MatImp = FALSE,
IP = NULL, IRT.PModel = "GRM", Ability = NULL, Ability.PModel = "EAP")
"Hotdeck", "NPModel" (default), and "PModel".IP=NULL). The options available are "PCM", "GPCM", and "GRM" (default).matrix.
In case no ability parameters are available then Ability=NULL.Ability=NULL). The options available are "EB", "EAP" (default), and "MI".G person-fit statistic to polytomous items, Gpoly. The idea is based on the so-called item-step difficulty, which is the probability of moving from answer category $(c)$ to answer category $(c+1)$ ($c=0,\ldots,Ncat-2$).Just like G, Gpoly depends on the test length. Emons (2008) developed Gnormed.poly, which is a normalized version of Gpoly.
Aberrant response behavior is (potentially) indicated by large values of Gpoly/Gnormed.poly (i.e., in the right tail of the sampling distribution).
The number of answer options, Ncat, is the same for all items.
Gpoly reduces to G, and Gnormed.poly reduces to Gnormed, when Ncat=2.
Missing values in matrix are imputed by one of three single imputation methods: Hotdeck imputation (NA.method = "Hotdeck"), nonparametric model imputation (NA.method = "NPModel"), and parametric model imputation (NA.method = "PModel"); see Zhang and Walker (2008).
IRT.PModel = "PCM","GPCM", or"GRM"). Item parameters (IP) and ability parameters (Ability) may be provided for this purpose (otherwise the algorithm finds estimates for these parameters).Karabatsos, G. (2003) Comparing the Aberrant Response Detection Performance of Thirty-Six Person-Fit Statistics. Applied Measurement In Education, 16(4), 277--298.
Meijer, R. R. (1994) The number of Guttman errors as a simple and powerful person-fit statistic. Applied Psychological Measurement, 18(4), 311--314.
Molenaar, I. W. (1991) A weighted Loevinger H-coefficient extending Mokken scaling to multicategory items. Kwantitatieve Methoden, 12(37), 97--117.
Zhang, B., and Walker, C. M. (2008) Impact of missing data on person-model fit and person trait estimation. Applied Psychological Measurement, 32(6), 466--479.
G, Gnormed# Load the physical functioning data (polytomous item scores):
data(PhysFuncData)
# Compute the Gpoly scores:
Gpoly.out <- Gpoly(PhysFuncData, Ncat=3)
# Compute the Gnormed.poly scores:
Gnormedpoly.out <- Gnormed.poly(PhysFuncData, Ncat=3)Run the code above in your browser using DataLab