where θ is the value of the latent variable
for a person, a is the discrimination parameter for
the item, P is the IRF for the person and item, and
Q=1-P. For the 1PL and 2PL models, the expression
reduces to a^2PQ.
Usage
iif(ip, x = NULL)
Arguments
ip
Item parameters: a matrix with one row per
item, and three columns: [,1] item discrimination
a, [,2] item difficulty b, and [,3] asymptote
c.
x
The values of the latent variable (θ
in the equation above), at which the IIF will be
evaluated. If not given, 99 values spaced evenly between
-4 and +4 will be used, handy for plotting.
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 x
f
A matrix containing the IIF values: persons
(values of (x) as rows and items as columns