Document ID: EPA-HQ-OAR-2011-0135-0636
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2013-04-17T04:00Z

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.2f
                              Final Model Fitting
                   Non-Methane Organic Gases (NMOG) (Bag 3)

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

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

                                       
                                     Full
                                    FM4[1]
                                      FM5
                                      FM6
                                      FM7
                                      FM8
                                      FM9
                                     FM10
                                     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
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                      ●
                                  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] denotes "Full minus 4, etc."

NMOG (Bag 3): Model fitting history, starting with the 16-term extended model.
                                Fit Parameters

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

                                                                           Dev.
                                                                              d
                                                                    Pr>χ[2]
Full Model
                                                                             16
                                                                       2605.071

                                                                               
                                                                               
                                                                               
FM4
                                                                             12
                                                                       2605.748

0.677
                                                                              4
0.954
FM5
                                                                             11
                                                                       2605.753

0.005
                                                                              1
0.944
FM6
                                                                             10
                                                                       2606.328

0.575
                                                                              1
0.448
FM7
                                                                              9
                                                                       2607.179

0.851
                                                                              1
0.356
FM8
                                                                              8
                                                                       2607.668

0.489
                                                                              1
0.484
FM9
                                                                              7
                                                                       2608.221

0.553
                                                                              1
0.457
FM10[2]
                                                                              6
                                                                       2608.338

0.117
                                                                              1
0.732

                                                                               

                                                                               
                                                                               
                                                                               
[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.

NMOG (Bag 3): Coefficients and Tests of Effect for the Full and Reduced Models, with respect to the 16-term extended model (NOTE: model fitting with respect to the 11-term design model gives the same results).