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Re: st: What grouping should I use for clogit?


From   Klaus Pforr <kpforr@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: What grouping should I use for clogit?
Date   Wed, 25 Jan 2012 10:53:25 +0100

<>
Dear Hadji,

could you be a litte bit more specific with your experimtal design, at least with the literature? The point why I ask this is, that if you randomize the important parts, you dont need fixed effects models, and can use pooled or random effects models, which have can have more advantages, provided that you exogenize the important other variables with a good experimental design.

With regard to the statistical model, I'm still dont understand what the choice sets for each respondent are. Is this comparable to a multilevel model? To be more specific, do you have multinomial choice for your respondents over choice sets and choices?

I think, as you probably randomize the respondents, you can ignore individual fixed effects, and have to think about these choice sets, for which you probably could use fixed effects. This means you would use the choice set ids as the group var. But this rests on my guessing of your situation, so maybe I'm wrong.

best

Klaus

Am 25.01.2012 05:48, schrieb Hadji Cortez Jalotjot:
Hi Klaus!

Thanks for the response.


My experimental design is based on what is described by Bunch (1996). A starting design is generated. I used R to generated an optimal
design.  This starting design served as the first alternative in my choice
experiment.  A foldover of the starting design is the second alternative.
Generic attributes were used.


My
dataset looks like this (this is for respondent 1):
respno - id of each respondent
obsid - same number means it belong to
the same choice set
choice - dummy var YES or No
the rest are the explanatory variables (attributes of a vehicle)


respno obsid choice eng1_GAS eng2_DIE eng3_LPG eng4_HEV eng5_ELE pp1_700K pp2_1M pp3_more1M range1_more450 range2_450 range3_200 c100km1_400 c100km2_600 incentv1_WITH incentv2_NO emis1_same emis2_80 NONE
1 1 1 0 0 0 0 1 0 1 0 0 1 0 1 0 1 0 0 1 0
1 1 0 0 0 0 1 0 1 0 0 1 0 0 0 1 0 1 1 0 0
1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 2 1 0 0 0 1 0 1 0 0 1 0 0 1 0 1 0 0 1 0
1 2 0 0 0 1 0 0 0 0 1 0 0 1 0 1 0 1 1 0 0
1 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 3 1 0 1 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 0
1 3 0 1 0 0 0 0 0 1 0 0 0 1 0 1 0 1 1 0 0
1 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 4 1 0 0 1 0 0 0 0 1 1 0 0 0 1 0 1 1 0 0
1 4 0 0 1 0 0 0 0 1 0 0 0 1 1 0 1 0 0 1 0
1 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 5 0 0 1 0 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0
1 5 0 1 0 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0
1 5 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 6 1 0 0 1 0 0 0 1 0 1 0 0 1 0 1 0 0 1 0
1 6 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 1 1 0 0
1 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 7 0 0 0 0 1 0 0 1 0 1 0 0 1 0 0 1 1 0 0
1 7 1 0 0 1 0 0 1 0 0 0 0 1 0 1 1 0 0 1 0
1 7 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 8 0 1 0 0 0 0 0 1 0 0 0 1 1 0 0 1 1 0 0
1 8 1 0 0 0 0 1 1 0 0 0 1 0 0 1 1 0 0 1 0
1 8 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 9 0 1 0 0 0 0 0 0 1 0 1 0 1 0 1 0 1 0 0
1 9 1 0 0 0 0 1 0 1 0 1 0 0 0 1 0 1 0 1 0
1 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 10 1 0 0 1 0 0 0 1 0 0 1 0 0 1 1 0 0 1 0
1 10 0 0 1 0 0 0 1 0 0 1 0 0 1 0 0 1 1 0 0
1 10 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1


My dependent variable is choice.
I understand clogit analyzes the data by
groups.
So which should I assign as group? Each
individual is the group (respno) OR each choice experiment (obsid)?
Thanks!
  Hadji




----- Original Message -----
From: Klaus Pforr<kpforr@googlemail.com>
To: statalist@hsphsun2.harvard.edu
Cc:
Sent: Tuesday, January 24, 2012 8:11 PM
Subject: Re: st: What grouping should I use for clogit?

Dear Hadji,

could tell a little bit more about your data, and the experimental
design? A data example would be helpful.

best

Klaus

Am 23.01.2012 07:46, schrieb Hadji Cortez Jalotjot:
I am estimating a choice model using the clogit command.  Data is from a choice experiment.

Each respondent was shown 10 choice sets.  Each choice set has 3 choices.

So basically, each respondent corresponds to 30 rows of observations.

My question is, should the respondents (respno) be my group for the clogit?  or should I treat each choice as the "group"?

Any suggestions or explanations are appreciated.

Hadji


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Klaus Pforr
MZES AB - A
Universität Mannheim
D - 68131 Mannheim
Tel:  +49-621-181 2797
fax:  +49-621-181 2803
URL:  http://www.mzes.uni-mannheim.de

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