st: asclogit with choice choice sets that vary across individuals

[Maria Ana Vitorino <vitorino@wharton.upenn.edu>]

Dear statalist users,

I'm trying to estimate a conditional logit model using asclogit. In my data, I have individuals with different choice sets. 

This is an example with a structure similar to what I have in my data:

id   univ   dist   choi
1	1	23	0
1	2	24	1
1	3	45	0
2	1	33	0	
2	3	5	1	
2	4	10	0
2	8	34	0
...
...

where id=individual's id, univ=university chosen, dist=distance from individual i to univ j and choi=choice.

Different individuals have different choice sets because otherwise the number of rows in the data would be too large (I have many individuals and universities). So, I assume that the choice set of each individual only includes the universities in a radius of 50 miles from where the individual lives.

The book "Microeconometrics Using Stata" says that "The asclogit command allows the choice set to vary across individuals".

I have 2 questions:

1) Can the command asclogit be actually used to estimate a conditional logit model with data like the one above (in which we have individuals with different choice sets)?

2) Do the choice sets of the individuals have to have at least one of the alternatives which is always common across the individuals? If not, how can one set a base alternative?
For example: asclogit choi dist, case(id)  alternatives (univ) basealternative(1) 

Any comments or suggestions are appreciated.
Thanks!
Ana




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