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Re: st: DiD


From   inggrid <[email protected]>
To   [email protected]
Subject   Re: st: DiD
Date   Wed, 30 Mar 2011 01:39:18 +0800 (SGT)

Dear Federico,


I have changed the variable of treat. As your suggestion, by ignoring year, I give a value of 1 to the individuals with the same id (2000 and 2007). But, STATA still dropped my interaction variable. Indeed, my data sets are unbalanced panel with a larger sample in 2007.

id	year	y   program   treat  post05  treat_post05
1	2000	10	0	0	0	0
2	2000	20	0	0	0	0
3	2000	30	0	0	0	0
4	2000	40	0	1	0	0
5	2000	50	0	1	0	0
6	2000	60	0	1	0	0
1	2007	70	0	0	1	0
2	2007	80	0	0	1	0
3	2007	90	0	0	1	0
4	2007	100	1	1	1	1
5	2007	110	1	1	1	1
6	2007	120	1	1	1	1
7	2007	130	0	0	1	0
8	2007	140	0	0	1	0
9	2007	150	0	0	1	0

Thanks in advance.


Best regards,
Inggrid
--- On Tue, 3/29/11, [email protected] <[email protected]> wrote:

> From: [email protected] <[email protected]>
> Subject: Re: st: DiD
> To: [email protected]
> Date: Tuesday, March 29, 2011, 10:33 PM
> I see many problems. First of all, I
> would expect an identifier, and to find it twice for each
> value (1 for year 2000 and 1 for year 2007). The only
> variable that could be an identifier is "y", but it doesn't
> respect this charachteristic. Then, you have 3 variables
> that are absolutely identical ("treat", "program" and
> "treat_post05").  So these commands:
> 
> > gen treat=(program!=0)
> > gen treat_post05 = treat*post05
> 
> are unuseful because they just generate clones of
> "program", because "program" is always equal to 1 (when
> different from 0) and is always equal to 0 for year 2000.
> Federico
> 
> ----- Messaggio originale -----
> Da: inggrid <[email protected]>
> Data: Tuesday, March 29, 2011 17:13
> Oggetto: Re: st: DiD
> A: [email protected]
> 
> > Hello again,
> > 
> > I have found my problem. To clarify everything, I am
> repeating 
> > my case. I have a two period panel data, 2000 and
> 2007. In 2005, 
> > there was a policy reform. Therefore, I can identify
> the 
> > participants by using data from 2007. I name it as 
> > "program".Then, the treated group is equal to
> "program". I 
> > generated treat_post05, an interaction dummy (the
> treatment 
> > effect).Consequently, treat_post05=treat.
> > 
> > Here is the example:
> > year    y   
> program    treat   
> post05    treat_post05
> > 2000    10   
> 0    0    0   
> 0
> > 2000    20   
> 0    0    0   
> 0
> > 2000    30   
> 0    0    0   
> 0
> > 2000    40   
> 0    0    0   
> 0
> > 2000    50   
> 0    0    0   
> 0
> > 2000    60   
> 0    0    0   
> 0
> > 2007    70   
> 0    0    1   
> 0
> > 2007    80   
> 0    0    1   
> 0
> > 2007    90   
> 0    0    1   
> 0
> > 2007    100   
> 1    1    1   
> 1
> > 2007    110   
> 1    1    1   
> 1
> > 2007    120   
> 1    1    1   
> 1
> > 
> > 
> > Basically, I can use the the simple t-test. But, I
> still need to 
> > include some control variables.
> > 
> > Any idea how to solve this?
> > 
> > Many thanks beforehand.
> > 
> > Best regards,
> > Inggrid
> > 
> > 
> > --- On Tue, 3/29/11, [email protected]
> 
> > <[email protected]>
> wrote:
> > 
> > > From: [email protected]
> <[email protected]>
> > > Subject: Re: st: DiD
> > > To: "inggrid" <[email protected]>
> > > Cc: [email protected],
> [email protected]
> > > Date: Tuesday, March 29, 2011, 7:06 PM
> > > > gen post05 = year>2000
> > > > gen treat_post05 = treat*post05
> > > 
> > > > note: post05 omitted because of
> collinearity
> > > > note: treat_post05 omitted because of
> collinearity
> > > 
> > > May be "post05" has been omitted because it's
> always equal
> > > to 1, and treat_post05 because it's always equal
> to "treat".
> > > I guess you misspecified the condition of post05
> (it
> > > shouldn't be "year>2000", but "year>2004"
> or 
> > > "year>2005"). 
> > > Federico
> > > *
> > > *   For searches and help try:
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> > > 
> > 
> > 
> >       
> > 
> > *
> > *   For searches and help try:
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> > *   http://www.stata.com/support/statalist/faq
> > *   http://www.ats.ucla.edu/stat/stata/
> 
> *
> *   For searches and help try:
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> *   http://www.ats.ucla.edu/stat/stata/
> 


      

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