nrm-methods {plink} | R Documentation |
This function computes the probability of responding in a specific category for one or more items for a given set of theta values using the nominal response model.
nrm(x, cat, theta = seq(-4,4,0.05), ...) ## S4 method for signature 'matrix', 'numeric' nrm(x, cat, theta, ...) ## S4 method for signature 'data.frame', 'numeric' nrm(x, cat, theta, ...) ## S4 method for signature 'list', 'numeric' nrm(x, cat, theta, ...) ## S4 method for signature 'irt.pars', 'ANY' nrm(x, cat, theta, ...) ## S4 method for signature 'sep.pars', 'ANY' nrm(x, cat, theta, ...)
x |
Object containing item parameters. See below for more details. |
cat |
vector identifying the number of response categories for each item |
theta |
vector of theta values for which probabilities will be computed.
If theta is not specified, an equal interval range of values from -4 to 4 is used
with an increment of 0.05 |
... |
further arguments passed to or from other methods |
Returns an object of class irt.prob
NA
. The remaining columns are for the
category difficulty parameters. Similarly, items with fewer response categories
than the maximum should have NA
s in the remaining cells. For example, for
one four category and one five category item, the first four columns for the four
response item would include the discrimination parameters. The fifth column for
this item would be NA
. The next four columns would include the category
difficulty values, and the last column would be NA
. NA
. For example, for one four category and one five
category item, the first four columns for the four response item in the first list
element would include the discrimination parameters. The fifth column for
this item would be NA
.The first four columns for the four response item in
the second list element would include the category difficulty parameters. The fifth
column for this item would be NA
. "irt.pars"
. If x
contains
dichotomous items or items associated with another polytomous model, a warning
will be displayed stating that probabilities will be computed for the nrm
items only. If x
contains parameters for multiple groups, a list of
"irt.prob"
objects will be returned.sep.pars
. If x
contains
dichotomous items or items associated with another polytomous model, a warning
will be displayed stating that probabilities will be computed for the nrm
items only.Jonathan P. Weeks weeksjp@gmail.com
Bock, R.D. (1972) Estimating item parameters and latent ability when responses are scored in two or more nominal categories. Psychometrika, 37(1), 29-51.
Bock, R.D. (1996) The nominal categories model. In W.J. van der Linden & Hambleton, R. K. (Eds.) Handbook of Modern Item Response Theory. New York: Springer-Verlag
Kolen, M. J., & Brennan, R. L. (2004) Test Equating, Scaling, and Linking. New York: Springer
mixed:
compute probabilities for mixed-format items
plot:
plot item characteristic/category curves
irt.prob
, irt.pars
, sep.pars:
classes
## Item parameters from Bock (1972, p. 46,47) a <- matrix(c(.905, .522, -.469, -.959, NA, .828, .375, -.357, -.079, -.817), 2,5,byrow=TRUE) c <- matrix(c(.126, -.206, -.257, .336, NA, .565, .865, -1.186, -1.199, .993), 2,5,byrow=TRUE) pars <- cbind(a,c) x <- nrm(pars, c(4,5)) plot(x,auto.key=list(space="right"))