why nonparametric models are used? why not use semiparametric modeling why use semiparametric or nonparametric models why semi-parametric model why use semi-parametrics why semiparametric model why is it necessary to use a nonparametric model? why use nonparametric models why is nonparametric model important why semi parametric model why use semi parametric why semi or nonparametric model why is it necessary to use nonparametric models why are nonparametric models useful why are semi parametrics useful why is a semi-nonparametric model useful? why nonparametric model why use nonparametric model why is a semiparametric model useful why semi-parametric models