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Re: st: DiD


From   [email protected]
To   [email protected]
Subject   Re: st: DiD
Date   Tue, 29 Mar 2011 17:33:31 +0200

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
> > *
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> > 
> 
> 
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