Item information function
The item information function (IIF) for the 3PL model can be computed as
I(θ) = a^2\frac{Q(θ)}{P(θ)}≤ft[\frac{P(θ)-c}{1-c}\right]^2,
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.
iif(ip, items = NULL, x = NULL)
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 (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. |
A common use of this function would be to obtain a plot of the IIF.
A list of:
x |
A copy of the argument |
f |
A
matrix containing the IIF values: persons (values of ( |
Ivailo Partchev
plot(iif(Scored2pl, items=1:3))
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