Unanimous votes are the
equivalent of test items that all subjects score “correct” (or
all subjects scores “incorrect”); since there is no variation
among the legislators/subjects, these votes/items provide no
information as to latent traits (ideology, preferences, ability). A
reasonably large number of rollcalls in any contemporary U.S. Congress
are unanimous.
Specific methods are provided for objects of class
rollcall
or matrix
.