From BILOG output, read in estimates of item parameters. Invoked
automatically when the model is estimated via
irtoys. If that is not
file must be a file produced with the
file; command in BILOG.
A list with three elements,
vcm for the parameter
estimates, their standard errors, and the variance-covariance matrix per item.
The first two are matrices with one row per item, and three columns: [,1] item
discrimination a, [,2] item difficulty b, and [,3] asymptote
c. For the 1PL and 2PL models, all asymptotes are equal to 0; for the
1PL, the discriminations are all equal but not necessarily equal to 1.