# Re: st: Re: Multinomial with Conditioning Variable unique to eachresponse?

 From Javier Miranda <[email protected]> To [email protected] Subject Re: st: Re: Multinomial with Conditioning Variable unique to eachresponse? Date Fri, 29 Jul 2005 13:25:26 -0400

Rafa,

Thank you very much. I think I understand.
Please do send that do file off the list if you can. I would love to look at it.

Best,
--Javi

R.E. De Hoyos wrote:

Javier,

You can model this using the -clogit- command.

Since the -mlogit- is a -clogit- where the parameters are allowed to differ across outcomes, you need to create dummy variables for each outcome and then interact them with the "characteristics of the individuals".

If you need an example, see:

http://www.ats.ucla.edu/stat/stata/examples/greene/greene19.htm

I also have a do-file that I can send you off the list.

Best,
Rafa

----- Original Message ----- From: "Javier Miranda" <[email protected]>
To: <[email protected]>
Sent: Friday, July 29, 2005 5:57 PM
Subject: Re: st: Re: Multinomial with Conditioning Variable unique to each response?

So, the way I understand it is I need a combination of multinomial and conditional logit formulations. I need a model where the choice outcome depends on the characteristics of the individual making the decision as well as the attributes of the choices (which influence the decision). I still need a normalization constraint so that the probabilities add up to 1. So what I need is a multinomial to estimate the probability of observing a particular event given a set of explanatory variables but where one of the explanatory variables describes attributes of the choices (not the individual making the choice). In that sense it is conditional on some of the attributes of the choice. The question is how do I model this?

R.E. De Hoyos wrote:

Javier,

I couldn't quite follow your question. In the multinomial logit model what varies across outcomes (in your case years) is the parameter not the independent variables, hence you do have a unique set of explanatory variables across alternatives for every unit of observation.

You said:
> More specifically, say I want to model the probability of an event

```occurring in any of four years, 1982, 1983, 1984 and 1985.
```

This sounds more like a conditional logit (-help clogit-). Although the conditional and the multinomial logit are mathematically the same, the nature of the problem they pretend to capture is completely different. In the conditional logit you are estimating the probability of occurrence of ANY event given a set of explanatory variables. In this case, the parameters are the same across outcomes and what varies is the explanatory variables. In the multinomial logit what you estimate is the probability of observing a particular event given a set of explanatory variables (given a normalization needed for identification, the results are interpreted as relative probabilities compared to the base outcome.)

I hope this helps,

Rafa
________________________
R.E. De Hoyos
Faculty of Economics
University of Cambridge
CB3 9DE, UK
www.econ.cam.ac.uk/phd/red29/

----- Original Message ----- From: "Javier Miranda" <[email protected]>
To: <[email protected]>
Sent: Friday, July 29, 2005 3:48 PM
Subject: st: Multinomial with Conditioning Variable unique to each response?

I want to estimate a Multinomial Logit Model where one of the conditioning variables is unique across alternatives.
More specifically, say I want to model the probability of an event occurring in any of four years, 1982, 1983, 1984 and 1985.
Now, say one of the conditioning variables is unque across alternatives; for example, assume the interest rate differs each year.
Now, if I estimate this model and generate the predicted probabilities I end up with a set of probibilites for each interest rate by year.
This is not right. Any suggestions as to what model I should be looking at?

Thanks Much
--javier miranda

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