Date: Mon, 25 Nov 2002 09:26:38 -0800
Reply-To: Dale McLerran <stringplayer_2@YAHOO.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Dale McLerran <stringplayer_2@YAHOO.COM>
Subject: Re: Need help on nested logit model!!
In-Reply-To: <7a5ed11d.0211240030.1e497974@posting.google.com>
Content-Type: text/plain; charset=us-ascii
The following datastep will construct a dataset which can be
passed into the MDC procedure.
data newdata;
set olddata;
array choices {4} brand1-brand4;
array pricebrand {4};
id = _n_';
do brand=1 to 4;
select = choices{brand};
price = pricebrand{brand};
output;
end;
keep id select brand price;
run;
The result will be a dataset which looks like this:
ID SELECT BRAND PRICE
1 1 1 3
1 0 2 4
1 0 3 1
1 0 4 2
2 0 1 ...
2 ... 2 ...
2 ... 3 ...
2 ... 4 ...
As far as providing you detail as to how to construct the code
for the MDC procedure, I prefer to allow students to look at the
documentation and puzzle over things for a while, consult with
other students as the situation warrants, or confess to their
professors that they just don't know how to complete the
assignment and would the professor be so kind as to spend a
little time clarifying some confusion or suggest what the student
might look at to get a better understanding of how to proceed.
I will point you to the online PDF documentation for the MDC
procedure:
http://www.sas.com/rnd/app/papers/mdc.pdf
The online PDF documentation for the QLIM procedure is at:
http://www.sas.com/rnd/app/papers/qlim.pdf
By the way, I was not aware of the (relatively) new MDC or QLIM
procedures, and so I searched the SAS web site for these keywords.
It took me all of 5 minutes to perform the search and read
enough of the documentation to answer the first of your questions.
I have fitted my own multinomial discrete choice models in the
past, and know enough about the structure of such models that it
did not take me long to review the documentation. I would
caution that the MDC procedure does not allow you to fit models
in which there are multiple instances of the response for each
subject, but I don't think that you will be getting into such
complexities right away.
Dale
--- wly <perfectle@HOTMAIL.COM> wrote:
> hi,there,
> i got a data arranged as the following form:
>
> brand1 brand2 brand3 brand4 pricebrand1 pricebrand2 pricebrand3
> pricebrand4
> 1 0 0 0 3 4 1 2
> 0 . . . . . . .
> . . . . . . . .
>
> because it seems to me that it's very diffcult to rearrange this data
> for the form needed in SAS, anybody can tell me how to do that and
> analysis this daat with PROC MDC or PROC QLIM ?? examples in detail
> will be deeply appreciated!
>
> thanks a lot!!
=====
---------------------------------------
Dale McLerran
Fred Hutchinson Cancer Research Center
mailto: dmclerra@fhcrc.org
Ph: (206) 667-2926
Fax: (206) 667-5977
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