Assessing the Effect of Five Gasoline Properties on Exhaust Emissions from Light-Duty Vehicles certified to Tier-2 Standards
                                       
                       Analysis of Data from EPA Phase 3
                                       
                                       
                                (EPAct/V2/E-89)

                                 Appendix I.3f
                              Final Model Fitting
                    Non-methane Hydrocarbons (NMHC) (Bag 3)


No. Observations:			   837
No. Vehicles:		  		     15   
No. censored measurements:		   119
No. missing measurements:		       0
No. measurements removed:		       0
Model Type:				Tobit regression








I.3f.1  Model Fitting based on the 11-term design model.

Model fitting for the 11-term design model gives results identical to those for the 16-term extended model, as presented below.
I.3f.2 Model Fitting based on the 16-term extended model.

    Models fit for NMHC (Bag 3): (Grand Intercept not fit by Tobit models).
Model Term
                                   Notation
                                     Model

                                       
                                     Full
                                    FM6[1]
                                      FM8
                                      FM9
                                     FM10
                                     FM11
                                     etOH
Ze
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                     Arom
Za
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      x
                                      RVP
Zr
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      T50
Z5
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      T90
Z9
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                 etOH x etOH
ZZee
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                  T50 x T50
ZZ55
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                 etOH x Arom
ZZea
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                  etOH x RVP
ZZer
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                  etOH x T50
ZZe5
                                      ●
                                      ●
                                      x
                                       
                                       
                                       
                                  etOH x T90
ZZe9
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                       

                                       
                                       
                                       
                                       
                                       
                                       
                                  Arom x RVP
ZZar
                                      ●
                                      ●
                                      x
                                       
                                       
                                       
                                  Arom x T50
ZZa5
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                  Arom x T90
ZZa9
                                      ●
                                      ●
                                      ●
                                      x
                                       
                                       
                                  T50 x T90
ZZ59
                                      ●
                                      x
                                       
                                       
                                       
                                       
                                  RVP x T90
ZZr9
                                      ●
                                      ●
                                      ●
                                      ●
                                      x
                                       





1  Indicates "Full minus 6," etc.

NMHC (Bag 3): Model fitting history, starting with the 17-term extended model.
                                Fit Parameters

                             Test with respect to
                                Previous Model
Model
                                                                         p-1[1]
                                     -2lnL


                                                                           Dev.
                                                                              d
                                                                    Pr>χ[2]
Full Model
                                                                             16
                                   2447.661


                                                                               
                                                                               
                                                                               
FM6
                                                                             10
                                   2448.148


                                     0.487
                                       6
                                     0.998
FM8
                                                                              8
                                   2449.275


                                     1.127
                                       2
                                     0.569
FM8
                                                                              7
                                   2449.727


                                     0.452
                                       1
                                     0.501
FM10
                                                                              6
                                   2450.108


                                     0.381
                                       1
                                     0.537
FM11[2]
                                                                              5
                                   2450.114


                                     0.006
                                       1
                                     0.938

                                                                               



                                                                               
                                                                               
                                                                               
[1] Total number of terms excludes the intercept, as the Tobit
Models do not fit intercepts.
[2] Best fit with respect to the 16-term extended model.





NMHC (Bag 3): Coefficients and Tests of Effect for the Full and Reduced Models, with respect to the 16-term extended model.



