The Objective Function Value (OFV), No. of Parameters, Parameter Estimations, and Measures of Performance for the Hierarchical Model Derived from the Control Group (without Nitrous Oxide) and for Three Competing Models (Sevoflurane-Additivity Model, Sevoflurane/Opioid-Additivity Model, and Sevoflurane-Additivity/Potentiation Model) Derived from the Total Dataset