Maximum likelihood weighted information (MLWI) and maximum posterior weighted information (MPWI)

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Description

This command returns the value of the likelihood (MLWI) or the posterior (MPWI) weighted information for a given item and an item bank (both under dichotomous and polytomous IRT models).

Usage

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MWI(itemBank, item, x, it.given, model = NULL, lower = -4, upper = 4, nqp = 33, 
 	type = "MLWI", priorDist = "norm", priorPar = c(0, 1), D = 1)
 

Arguments

itemBank

numeric: a suitable matrix of item parameters. See Details.

item

numeric: the item (referred to as its rank in the item bank) for which the expected information must be computed.

x

numeric: a vector of item responses, coded as 0 or 1 only (for dichotomous items) or from 0 to the number of response categories minus one (for polytomous items).

it.given

numeric: a suitable matrix of item parameters for previously administered items. The number of rows of it.given must be equal to the length of x.

model

either NULL (default) for dichotomous models, or any suitable acronym for polytomous models. Possible values are "GRM", "MGRM", "PCM", "GPCM", "RSM" and "NRM". See Details.

lower

numeric: the lower bound for numerical integration (default is -4).

upper

numeric: the upper bound for numerical integration (default is 4).

nqp

numeric: the number of quadrature points (default is 33).

type

character: the type of information to be computed. Possible values are "MLWI" (default) and "MPWI". See Details.

priorDist

character: the prior ability distribution. Possible values are "norm" (default) for the normal distribution, and "unif" for the uniform distribution. Ignored if type is not "MPWI".

priorPar

numeric: a vector of two components with the prior parameters. If priorDist is "norm", then priorPar contains the mean and the standard deviation of the normal distribution. If priorDist is "unif", then priorPar contains the bounds of the uniform distribution. The default values are 0 and 1 respectively. Ignored if type is not "MPWI".

D

numeric: the metric constant. Default is D=1 (for logistic metric); D=1.702 yields approximately the normal metric (Haley, 1952). Ignored if model is not NULL.

Details

Both the MLWI (Veerkamp and Berger, 1997) and the MPWI (van der Linden, 1998; van der Linden and Pashley, 2000) can be used as rules for selecting the next item in the CAT process (see also Choi and Swartz, 2009), both under dichotomous and polytomous IRT models. This command serves as a subroutine for the nextItem function.

Dichotomous IRT models are considered whenever model is set to NULL (default value). In this case, itemBank must be a matrix with one row per item and four columns, with the values of the discrimination, the difficulty, the pseudo-guessing and the inattention parameters (in this order). These are the parameters of the four-parameter logistic (4PL) model (Barton and Lord, 1981).

Polytomous IRT models are specified by their respective acronym: "GRM" for Graded Response Model, "MGRM" for Modified Graded Response Model, "PCM" for Partical Credit Model, "GPCM" for Generalized Partial Credit Model, "RSM" for Rating Scale Model and "NRM" for Nominal Response Model. The itemBank still holds one row per item, end the number of columns and their content depends on the model. See genPolyMatrix for further information and illustrative examples of suitable polytomous item banks.

Under polytomous IRT models, let k be the number of administered items, and set x_1, ..., x_k as the provisional response pattern (where each response x_l takes values in \{0, 1, ..., g_l\}). Set also I_j(θ) as the information function of item j evaluated at θ, and set L(θ | x_1, ..., x_k) as the likelihood function evaluated at θ, given the provisional response pattern. Then, the LWI for item j is given by

LWI_j = \int I_j(θ) L(θ | x_1, ..., x_k) dθ

and the PWI by

PWI_j = \int I_j(θ) π(θ) L(θ | x_1, ..., x_k) dθ

where π(θ) is the prior distribution of the ability level.

In case of dichotomous IRT models, all g_l values reduce to 1, so that item responses x_l equal either 0 or 1. But except from this difference, the previous definitions of LWI and PWI remain valid.

These integrals are approximated by the integrate.catR function. The range of integration is set up by the arguments lower, upper and nqp, giving respectively the lower bound, the upper bound and the number of quadrature points. The default range goes from -4 to 4 with length 33 (that is, by steps of 0.25).

The argument type defines the type of information to be computed. The default value, "MLWI", computes the MLWI value, while the MPWI value is obtained with type="MPWI". For the latter, the priorDist and priorPar arguments fix the prior ability distribution. The normal distribution is set up by priorDist="norm" and then, priorPar contains the mean and the standard deviation of the normal distribution. If priorDist is "unif", then the uniform distribution is considered, and priorPar fixes the lower and upper bounds of that uniform distribution. By default, the standard normal prior distribution is assumed. This argument is ignored whenever method is not "MPWI".

The provisional response pattern and the related item parameters are provided by the arguments x and it.given respectively. The target item (for which the maximum information is computed) is given by its rank number in the item bank, through the item argument.

Note that the provisional response pattern x can also be set to NULL (which is useful when the number nrItems of starting items is set to zero). In this case, it.given must be a matrix with zero rows, such as e.g., itemBank[NULL,]. In this very specific configuration, the likelihood function L(θ | x_1, ..., x_k) reduces to the constant value 1 on the whole θ range (that is, a uniform likelihood).

Value

The required (likelihood or posterior) weighted information for the selected item.

Author(s)

David Magis
Department of Education, University of Liege, Belgium
david.magis@ulg.ac.be

References

Barton, M.A., and Lord, F.M. (1981). An upper asymptote for the three-parameter logistic item-response model. Research Bulletin 81-20. Princeton, NJ: Educational Testing Service.

Choi, S. W., and Swartz, R. J. (2009). Comparison of CAT item selection criteria for polytomous items. Applied Psychological Measurement, 32, 419-440. doi: 10.1177/0146621608327801

Haley, D.C. (1952). Estimation of the dosage mortality relationship when the dose is subject to error. Technical report no 15. Palo Alto, CA: Applied Mathematics and Statistics Laboratory, Stanford University.

Magis, D., and Raiche, G. (2012). Random Generation of Response Patterns under Computerized Adaptive Testing with the R Package catR. Journal of Statistical Software, 48 (8), 1-31. URL http://www.jstatsoft.org/v48/i08/

van der Linden, W. J. (1998). Bayesian item selection criteria for adaptive testing. Psychometrika, 63, 201-216. doi: 10.1007/BF02294775

van der Linden, W. J., and Pashley, P. J. (2000). Item selection and ability estimation in adaptive testing. In W. J. van der Linden and C. A. W. Glas (Eds.), Computerized adaptive testing. Theory and practice (pp. 1-25). Boston, MA: Kluwer.

Veerkamp, W. J. J., and Berger, M. P. F. (1997). Some new item selection criteria for adaptive testing. Journal of Educational and Behavioral Statistics, 22, 203-226. doi: 10.3102/10769986022002203

See Also

Ii, nextItem, integrate.catR, genPolyMatrix

Examples

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## Dichotomous models ##

 # Loading the 'tcals' parameters 
 data(tcals)

 # Selecting item parameters only
 bank <- as.matrix(tcals[,1:4])
 
  # Selection of two arbitrary items (15 and 20) of the
 # 'tcals' data set
 it.given <- bank[c(15, 20),]

 # Creation of a response pattern
 x <- c(0, 1)

 # MLWI for item 1
 MWI(bank, 1, x, it.given)

 # MPWI for item 1
 MWI(bank, 1, x, it.given, type = "MPWI")

 # MLWI for item 1, different integration range
 MWI(bank, 1, x, it.given, lower = -2, upper = 2, nqp = 20)

 # MPWI for item 1, uniform prior distribution on the range [-2,2]
 MWI(bank, 1, x, it.given, type = "MPWI", priorDist = "unif", priorPar = c(-2, 2))


## Polytomous models ##

 # Generation of an item bank under GRM with 100 items and at most 4 categories
 m.GRM <- genPolyMatrix(100, 4, "GRM")
 m.GRM <- as.matrix(m.GRM)

 # Selection of two arbitrary items (15 and 20) 
 it.given <- m.GRM[c(15, 20),]

 # Generation of a response pattern (true ability level 0)
 x <- genPattern(0, it.given, model = "GRM")

 # MLWI for item 1
 MWI(m.GRM, 1, x, it.given, model = "GRM")

 # MPWI for item 1
 MWI(m.GRM, 1, x, it.given, model = "GRM", type = "MPWI")

 # MLWI for item 1, different integration range
 MWI(m.GRM, 1, x, it.given, model = "GRM", lower = -2, upper = 2, nqp = 20)

 # MPWI for item 1, uniform prior distribution on the range [-2,2]
 MWI(m.GRM, 1, x, it.given, model = "GRM", type = "MPWI", priorDist = "unif", 
 priorPar = c(-2, 2))


 # Generation of an item bank under PCM with 20 items and 4 categories
 m.PCM <- genPolyMatrix(20, 4, "PCM", same.nrCat = TRUE)
 m.PCM <- as.matrix(m.PCM)

 # Selection of two arbitrary items (15 and 20) 
 it.given <- m.PCM[c(15, 20),]

 # Generation of a response pattern (true ability level 0)
 x <- genPattern(0, it.given, model = "PCM")

  # MLWI for item 1
 MWI(m.PCM, 1, x, it.given, model = "PCM")

 # MPWI for item 1
 MWI(m.PCM, 1, x, it.given, model = "PCM", type = "MPWI")

 # MLWI for item 1, different integration range
 MWI(m.PCM, 1, x, it.given, model = "PCM", lower = -2, upper = 2, nqp = 20)

 # MPWI for item 1, uniform prior distribution on the range [-2,2]
 MWI(m.PCM, 1, x, it.given, model = "PCM", type = "MPWI", priorDist = "unif", 
 priorPar = c(-2, 2))
 

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