PlackettLuce: itempar.PlackettLuce – R documentation

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itempar.PlackettLuce

Extract Item Parameters of Plackett-Luce Models

Description

Methods for itempar to extract the item parameters (worth or log-worth) from a Plackett-Luce model or tree. In the case of a tree, item parameters are extracted for each terminal node.

Usage

## S3 method for class 'PlackettLuce'
itempar(object, ref = NULL, alias = TRUE, vcov = TRUE, log = FALSE, ...)

## S3 method for class 'pltree'
itempar(object, ...)

## S3 method for class 'PLADMM'
itempar(object, ref = NULL, alias = TRUE, vcov = TRUE, log = FALSE, ...)

Arguments

`object`	a fitted model object as returned by `PlackettLuce`, `pladmm`, or `pltree`.
`ref`	a vector of labels or position indices of item parameters which should be used as restriction/for normalization. If `NULL` (the default), all items are used with a zero sum (`log = TRUE`) or unit sum (`log = FALSE`) constraint.
`alias`	logical. If `TRUE` (the default), the aliased parameter is included in the return vector (and in the variance-covariance matrix if `vcov = TRUE`). If `FALSE`, it is removed. If the restriction given in ref depends on several parameters, the first parameter of the restriction specified is (arbitrarily) chosen to be removed if alias is `FALSE`.
`vcov`	logical. If `TRUE` (the default), the (transformed) variance-covariance matrix of the item parameters is attached as attribute `vcov`. If `FALSE`, a `NA`-matrix is attached.
`log`	logical. Whether to return log-abilities (`TRUE`) or abilities (`FALSE`).
`...`	further arguments which are currently not used.

Value

An object of class "itempar", see itempar.

Examples

R <- matrix(c(1, 2, 0, 0,
              4, 1, 2, 3,
              2, 1, 1, 1,
              1, 2, 3, 0,
              2, 1, 1, 0,
              1, 0, 3, 2), nrow = 6, byrow = TRUE)
colnames(R) <- c("apple", "banana", "orange", "pear")

mod <- PlackettLuce(R)
coef(mod)

# equivalent to default coefficients, i.e. log abilities
itempar(mod, ref= 1, log = TRUE)

# abilities, normalized so abilities for apple and pear sum to 1
itempar(mod, ref = 1:2)

PlackettLuce

Plackett-Luce Models for Rankings

v0.4.0

GPL-3

Authors

Heather Turner [aut, cre] (<https://orcid.org/0000-0002-1256-3375>), Ioannis Kosmidis [aut] (<https://orcid.org/0000-0003-1556-0302>), David Firth [aut] (<https://orcid.org/0000-0003-0302-2312>), Jacob van Etten [ctb] (<https://orcid.org/0000-0001-7554-2558>)

Initial release