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# RE: st: calculate probability for clogit

 From Patty_FARE_Guelph Apichaya To statalist Subject RE: st: calculate probability for clogit Date Fri, 23 Apr 2010 13:05:41 +0000

Hi,

Could you give me an example? How I can code it for 2 choice?
I tried to code it but the program doesn't work.

asclogit  choice price brand labeling, case(choiceset) alternative( alt_choice)
variable alt_choice has replicate levels for one or more cases; this is not allowed

I look at your code and looked at how they code data in webuse choice, clear.
drop if car==3, is it mean I have to generate alternative 3 in the data set? because I have only 2alternatives.

However, when I look at the data set of -clogit- and -asclogit-. They are the same.
clogit  choice price brand labeling, group(choiceset)

I agree that the case or group variable in -clogit- I will use pair (choiceset).
For example, I have 32 choice set and 1 choice set has pair of alternatives (optionA and B)
This is that way that I code in my data set :

choiceset     alternatives
1                 1
1                 2
2                 1
2                 2
3                 1
3                 2
-
-
32                1
32                2
1                1

1                 2

2                 1

2                 2

3                 1

3                 2

-

-

32                1

32                2

I will repeat the choice set again for next individual.
Another point is should I continue choice set from 32 to 33 or should I repeat it from 1 to 32?

Thank a lots

Apichaya Lilavanichakul
MSc. Candidate
Department of Food Agricultural and Resource Economics
Ontario Agricultural College
University of Guelph
Guelph, ON

----------------------------------------
> Date: Fri, 23 Apr 2010 08:10:17 -0400
> Subject: Re: st: calculate probability for clogit
> From: sjsamuels@gmail.com
> To: statalist@hsphsun2.harvard.edu
>
> I should never post to Statalist in the middle of the night. I
> apologize for the brevity of the last message.
>
> -asclogit- worked for me in Stata 11 with two outcomes using the
> choice data set.
>
> ********************
> webuse choice, clear
> drop if car==3
> asclogit choice , casevars(sex) case(id) alternatives(car)
> tab car, gen(car)
> gen car2_sex =car2*sex //add interaction of person-level variable
> with alternative
> clogit choice car dealer car2_sex , group(id) //sex enters only in
> interaction
> *********************
> However I don't understand the pairwise design well-enough to be sure
> of what you should do. One guess is that the case or group variable
> should not be ID but "pair" and that to get proper standard errors you
> should bootstrap the command with ID as a cluster variable for the
> bootstrap. However, I think you need to consult somebody who knows
> more about these analyses than I do. If you come back a correct
> analysis in SAS, for example, we can probably help translate it into
> Stata.
>
> Steve
>
> On Fri, Apr 23, 2010 at 12:54 AM, Steve Samuels  wrote:
>> Sorry, you are on your own.  -asclogit- worked for me with two
>> alternatives in Version 11 examples with the web "choice" data set.,
>> but perhaps there's something special about your data, or you did not
>> have the proper format (2 records per person and option).   You can
>> get person-level variables into -clogit- by adding their interactions
>> with your alternative variable.    However you cannot use the -clogit-
>> data format for -asclogit-.  As I said this is not my area, so read
>> the manual entries.
>>
>> Good luck.
>> Steve
>>
>> On Thu, Apr 22, 2010 at 9:34 PM, Patty_FARE_Guelph Apichaya
>>  wrote:
>>> Hi,
>>>
>>>   I try to use -asclogit- but it has to have more than 2 alternatives in 1 choice set, so I cannot use this command in my analysis.
>>>  For the choice design, I use SAS software to design the pair of alternative and combination of factors in order to balance and give the optimal sets. I use clogit to analyze my choices and I want to know how I calculate probability the people choose each alternative in choice set.
>>>
>>> if I want to calculate personal factors, should I use -xtlogit- or which command it is appropriate?
>>>
>>> Thanks
>>>
>>> Apichaya Lilavanichakul
>>> MSc. Candidate
>>> Department of Food Agricultural and Resource Economics
>>> Ontario Agricultural College
>>> University of Guelph
>>> Guelph, ON
>>>
>>>
>>>
>>>> Date: Tue, 20 Apr 2010 16:12:44 -0400
>>>> Subject: Re: st: calculate probability for clogit
>>>> From: sjsamuels@gmail.com
>>>> To: statalist@hsphsun2.harvard.edu
>>>>
>>>>
>>>> 1. -asclogit-  might be a better choice than -clogit-, as it will more
>>>> easily include  person-level variables like gender, income, and sex.
>>>>
>>>> 2. Your setup does not identify the individual in any way. The
>>>> examples for -asclogit- and -clogit-  all use the individual as the
>>>> case or group variable. As "set" has only four levels, perhaps you can
>>>> include it as a person-level variable.
>>>>
>>>> 3. The examples in -asclogit- consider  alternatives based on one
>>>> attribute (factor).  You have three factors  and these generate 12 (=
>>>> 3 x 2 x 2)  possible options, with 66  possible pairwise comparisons.
>>>> You selected 32 of these,  divided into four sets.  I'm curious--is
>>>> there  a reference for this experimental design?  Is the choice of
>>>> comparisons and construction of the sets  optimal or balanced in some
>>>> sense?
>>>>
>>>> 4. For predicted probabilities, use  the  -pr- option in -asclogit- .
>>>>
>>>> Steve
>>>>
>>>> On Tue, Apr 20, 2010 at 9:39 AM, Patty_FARE_Guelph Apichaya
>>>>  wrote:
>>>>> Hi all,
>>>>>
>>>>>       I use STATA to analyze discrete choihce experiment. My choice design has 32 choice sets with each 2 options (A and B). Each option include 3 factors: price (13,15,17), brand (AA,BB), labeling (animal,plant). The choice set will look like this.
>>>>>                  Option A                           OptionB
>>>>>     price                    13                                       15
>>>>>     brand                   AA                                        BB
>>>>>    labeling          animal                               plant
>>>>>
>>>>>            From 32 choice sets is divide into 4 block with each 8 choice sets. Each individual (100 individuals) get 1 block (8 choice sets) and ask to choose between option A or B.
>>>>>
>>>>>     choice = 1 chosen option, 0 not chosen option
>>>>>     set = same for two alternatives for each set i.e. there are 32 choice sets, it is repeated number from 1 to 32 and start it
>>>>>           again for the next 32 choice sets.
>>>>>
>>>>> This is the code; clogit choice price brand labeling, group(set)
>>>>>
>>>>> I also want to include individual characteristics; gender, income, age. how I can do it?
>>>>>
>>>>> How I can calculate the probability from people choosing choice?
>>>>>
>>>>> Any suggestion would be great.
>>>>> Pat
>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Steven Samuels
>>>> sjsamuels@gmail.com
>>>> 18 Cantine's Island
>>>> Saugerties NY 12477
>>>> USA
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>>>> Fax:    206-202-4783
>>>>
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>>
>>
>>
>> --
>> Steven Samuels
>> sjsamuels@gmail.com
>> 18 Cantine's Island
>> Saugerties NY 12477
>> USA
>> Voice: 845-246-0774
>> Fax:    206-202-4783
>>
>
>
>
> --
> Steven Samuels
> sjsamuels@gmail.com
> 18 Cantine's Island
> Saugerties NY 12477
> USA
> Voice: 845-246-0774
> Fax: 206-202-4783
>
> *
> * For searches and help try:
> * http://www.stata.com/help.cgi?search
> * http://www.stata.com/support/statalist/faq
> * http://www.ats.ucla.edu/stat/stata/

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