Re: st: DiD

[inggrid <inggrid_ep@yahoo.com>]

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, federico.tedeschi@univr.it <federico.tedeschi@univr.it> wrote:

> From: federico.tedeschi@univr.it <federico.tedeschi@univr.it>
> Subject: Re: st: DiD
> To: "inggrid" <inggrid_ep@yahoo.com>
> Cc: statalist@hsphsun2.harvard.edu, federico.tedeschi@univr.it
> 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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