在不考虑a的情况下我的回归结果是正常且显著
diff patent_suc,t( dumpinter ) p( casetime ) cov( maxtfp size capital ) test
我想要研究加入a以后的结果于是尝试将a放入控制变量中
.diff patent_suc,t( dumpinter ) p( casetime ) cov( a maxtfp size capital) test
Number of observations (baseline): 602366
Before After
Control: 571863 - 571863
Treated: 30503 - 30503
602366 -
t-test at period = 0:
----------------------------------------------------------------------------------------------
Variable(s) | Mean Control | Mean Treated | Diff. | |t| | Pr(|T|>|t|)
---------------------+------------------+--------------+------------+---------+---------------
patent_suc | 1.121 | 0.888 | -0.233 | 2.30 | 0.0212**
a | 0.000 | 0.000 | 0.000 | . | .
maxtfp | 4.397 | 4.148 | -0.248 | 24.05 | 0.0000***
size | 5.405 | 5.257 | -0.148 | 19.62 | 0.0000***
capital | 0.077 | 0.080 | 0.003 | 1.87 | 0.0611*
----------------------------------------------------------------------------------------------
*** p<0.01; ** p<0.05; * p<0.1
不知道为什么a这一栏没有数据显示,想求问各位老师和同学是不是我DID模型理解错了,这里的变量a不应该在这个命令下使用
部分数据列示如下:
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- * Example generated by -dataex-. To install: ssc install dataex
- clear
- input double(year party_id) float(dumpinter casetime a maxtfp size capital)
- 2010 1207210 0 0 0 4.4024405 3.6888795 .17882326
- 2013 33119619 1 1 3.9676516 3.9676516 5.433722 .028345535
- 2000 1101910091 0 0 0 3.232003 . .
- 2004 1101910091 0 0 0 3.54374 5.733341 .02918006
- 2005 1101910091 0 0 0 3.5172274 5.332719 .04353831
- 2006 1101910091 0 0 0 3.5788324 5.332719 .04852101
- 2007 1101910091 0 0 0 4.0062785 5.087596 .05753561
- 2008 1101910091 0 0 0 3.860725 5.075174 .05877285
- 2010 1101910091 0 0 0 3.985518 5.087596 .0614109
- 2000 1101910105 0 0 0 3.3423824 . .
- 2001 1101910105 0 0 0 3.278029 . .
- 2002 1101910105 0 0 0 2.9427354 . .
- 2003 1101910105 0 0 0 2.1838508 . .
- 2002 1101910106 0 0 . . . .
- 2003 1101910106 0 0 0 2.7255075 . .
- 2004 1101910106 0 0 0 2.615981 7.700295 .006157428
- 2010 1101910106 0 0 0 2.7168915 7.367709 .008621673
- 2001 1101910112 0 0 0 3.418738 . .
- 2002 1101910112 0 0 0 4.0138016 . .
- 2003 1101910112 0 0 0 3.108391 . .
- end
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