iif {irtoys} | R Documentation |
Item information function
Description
The item information function (IIF) for the 3PL model can be computed as
where
is the value of the latent variable for a person,
is
the discrimination parameter for the item,
is the IRF for the person
and item, and
. For the 1PL and 2PL models, the expression
reduces to
.
Usage
iif(ip, items = NULL, x = NULL)
Arguments
ip |
Item parameters: the output of |
items |
The item(s) for which the information function is computed. If NULL (the default), irf for all items will be returned |
x |
The values of the latent variable ( |
Details
A common use of this function would be to obtain a plot of the IIF.
Value
A list of:
x |
A copy of the argument |
f |
A
matrix containing the IIF values: persons (values of ( |
Author(s)
Ivailo Partchev
See Also
Examples
plot(iif(Scored2pl, items=1:3))