eRm, numDeriv, graphics, grDevices, stats, methods, MASS,
splines, Matrix, lattice
eRm, psychotools, ltm, numDeriv, graphics, grDevices, stats,
methods, MASS, splines, Matrix, lattice, colorspace, psych
eRm, psychotools, ltm, numDeriv, graphics, grDevices, stats,
methods, MASS, splines, Matrix, lattice, rlang