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st: clogit w/ different choice set


From   "Eunkyeong Lee" <el223@cornell.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: clogit w/ different choice set
Date   Tue, 11 Sep 2007 16:38:26 -0400 (EDT)

Hi-
Hi-

I want to estimate patient's hospital choice model, using clogit, but
my problem arise because each patient has different hospital choice
sets.

For example, suppose patient#1 chose hosp#1 although she could choose
hospital#2 and #3. Then, the data set should be arranged as follows:
Y(choice=1)=X's (hospital characteristics such as distance to hospitals)
and hospital-specific dummy variables.

pat_id choice some X's hosp_opt1 hosp_opt2 hops_opt3
1        1                1        0           0
1        0                0        1           0
1        0                0        0           1

The model would be
clogit choice X's hosp_opt2 hosp_opt3, group(pat_id)

However, now patient#2 chose hosp#3 when her choice set has hosp#1,
hosp#4, hosp#5.

pat_id choice some X's hosp_opt1 hosp_opt2 hops_opt3 hops_opt4 hops_opt5
2        1                0        .           1         0         0
2        0                1        .           0         0         0
2        0                0        .           0         1         0
2        0                0        .           0         0         1

Now I have to estimate
clogit choice(Y) X's hosp_opt1 hosp_opt4 hosp_opt5, group(pat_id)

So basically, for each patient, the number of hospital-specific dummies
is different as well as the identification of the dummies.
Could anyone help me out how to estimate clogit model in this case? I've
looked at the STATA manual book, googled it, and did everything, but I
could not still figure this out. Thanks.

Eunkyeong

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