iif: Item information function
In lebebr01/irtoys-2: Simple interface to the estimation and plotting of IRT models

Description Usage Arguments Details Value Author(s) See Also Examples

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.

1	iif(ip, x = NULL)

`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.