[Limdep Nlogit List] Problem with Inclusive Value parameter inNested Logit Model.

Mon Apr 13 02:34:53 EST 2009

Dear Duggal,
Thank you for your suggestion. I tried to specify normalization at RU1 with the same starting value and obtained the IV parameters for Car and Nocar branches as 0.445036 and 1.48408, respectively. Both of these parameters are statistically significant at 99% confident level. However, the exit code of NLOGIT is 1 instead of 0. That means the estimation did not really converge. 
Using this result as starting value for another procedure (Adding Maxit =150 to syntax), the exit status is 3 (Error:   806: Line search does not improve fn. Exit iterations. Status=3) at iteration 110. The LLFs at entry and exit are -25517 and -25415, respectively. 
One of the possible reasons for the unconvergence that I guess is the unbalance in sample size of bundles in response variable. Sample size for each bundle is as follows:
Bundle0: 363
Bundel1: 1344
Bundel2: 13170
Bundle3: 10
Bundle4: 12406
Bundle5: 14
Bundle6: 281
Bundle7: 161.
In short, the bundles containing vehicle type Car are small in sample sizes. Any suggestion to overcome such kind of the problem?
Sincerely yours,

HO, Quoc Chinh.
Nagoya University, school of engineering
Faculty of Civil Engineering.

Email:   hoqchinh at yahoo.com.vn
            chinh at trans.civil.nagoya-u.ac.jp

--- Chủ nhật, 12/04/09, Mausam Duggal <DuggalM at mmm.ca> đã viết:

Từ: Mausam Duggal <DuggalM at mmm.ca>
Chủ đề: Re: [Limdep Nlogit List] Problem with Inclusive Value parameter inNested Logit Model.
Đến: "Limdep and Nlogit Mailing List" <limdep at limdep.itls.usyd.edu.au>
Ngày: Chủ nhật, 12 tháng 4, 2009, 22:04

Ho,

For starters, what happens if you specify normalization at RU1 instead of RU2. Ru1 is anyways preferred based on Hensher, Rose and Greene, Applied Choice Analysis, A Primer.

Thanks.

Mausam Duggal, MCIP, RPP

Senior Project Coordinator

MMM GROUP

100 Commerce Valley Drive West

Thornhill, ON Canada L3T 0A1

T: 905-882-4211, x6289

F: 905-882-7277

W: www.mmm.ca

-----Original Message-----
From: limdep-bounces at limdep.itls.usyd.edu.au [mailto:limdep-bounces at limdep.itls.usyd.edu.au] On Behalf Of ho quoc Chinh
Sent: Sunday, April 12, 2009 2:05 AM
To: limdep at limdep.itls.usyd.edu.au
Subject: [Limdep Nlogit List] Problem with Inclusive Value parameter inNested Logit Model.

Dear all,

I am fitting the Nested logit model with NLOGIT version 3.0.
As a response variable we have eight (08) alternatives. They are: 

None(bundle0), Bike only (bundle1), Motorcycle only
(bundle2), car only (bundle3), Bike and Motorcycle (bundle4), Bike and Car
(bundle5), Motorcycle and Car (bundle6) and All of these three vehicles (bundle7).
All attribute parameters are set to be alternative-specific.

The syntax of the model, which I use, is: 

NLOGIT;
Lhs= BUNDLE;

Choices=bundle0,
bundle1, bundle2, bundle3,bundle4, bundle5, bundle6, bundle7;

    Tree= Car(bundle3, bundle5, bundle6,
bundle7),

    NOcar(bundle0,
bundle1,bundle2,bundle4);

    Model: U(bundle0)=0/

    U(bundle1)=
b2*WORKER+b3*NONWORK+b4*CHILD+b6*INC+b8*PPDENS+b9*DIST/

    U(bundle2)=
b10+b11*WORKER+b12*NONWORK+b13*CHILD+b14*HOUSEOWN

                        +b15*INC
+b17*PPDENS +a2*HEADPRO/

    U(bundle4)=
b28+b29*WORKER+b30*NONWORK+b31*CHILD+b32*HOUSEOWN

                        +b33*INC+b34*MIXLAND+b35*PPDENS
+a4*HEADPRO/

    U(bundle3)= b20*HEADPRO/  

    U(bundle5)= b38+b42*INC +b44*PPDENS /

    U(bundle6)=b46+b50*HOUSEOWN+b51*INC+b53*PPDENS+b54*DIST+a6*HEADPRO/

    U(bundle7)=b55+b59*HOUSEOWN+b60*INC+b62*PPDENS
+a7*HEADPRO;

RU2;  

Tlg=0.00001       

$

And
after execution of the model, I obtain the estimates with NEGATIVE Inclusive Value
parameter for Car branch, which can been seen as follow: 

IV parameters, RU2 form =
mu(j|i),gamma(i)

 CAR        
-1.881354099       .11426681  -16.465  
.0000

 NOCAR       
8.594011416       1.1771514    7.301  
.0000

What does seem to be the problem? And how should we
understand the negative IV parameter since negative sign of IV parameter is in
fact contrary to the literature. 

Moreover, if we let NLOGIT do the above syntax by itself,
convergence cannot be obtained due to LLF improvement problem. Thus, I have
already employed sequential estimation to obtain the starting value for the
above Nested logit model. 

Any sharing of experience, references or hints are highly
appreciated.

Best regards,

HO, Quoc Chinh.

Nagoya
 University, school of
engineering

Faculty of Civil Engineering.

Email: hoqchinh at yahoo.com.vn

            chinh at trans.civil.nagoya-u.ac.jp

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