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st: Different sign in two model


From   Song Nhac <songnhac@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Different sign in two model
Date   Sun, 12 Jul 2009 22:17:00 +0700

Dear All,

I am a newcomer of Stata. I searched for a while in archives list but
there is no related topic to this, so I have a question about my
result:
I employed Weibull model and Log logic model to test my data, but, I
received two different sign in alpha and beta
In Weibull: beta= -.3503182 and alpha=2.669465 (negative in beta)
but in Log logic: beta= .8955857 and alpha= -.4768999 (negative in
alpha)- I expect beta is negative in this model but it did not.
 I use the same data set, in which the dependent variable is
(survival) as in attached data set. and independent variable is
(lenght)
I followed the guideline in "maximum likelihood estimation with stata-
3rd edition" to do those tests. So what could I explain for those
results?

Thank for your kindly support,
Best regards,
Ha Pham
id	run	length	hazard	survival
1	1	8	0.53	1
2	1	3	0.43	1
3	5	1	0.25	0
4	1	3	1.00	1
5	1	0	0	1
6	2	0	0	0
7	1	0	0	1
8	4	0	0	0
9	4	0	0	0
10	2	0	0	0
11	4	0	0	0
12	1	0	0	1
13	3	0	0	0
14	1	0	0	1
15	2	0	0	0
16	1	0	0	1



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