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From |
"FEIVESON, ALAN H. (AL) (JSC-SK) (NASA)" <alan.h.feiveson@nasa.gov> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: difference-in-difference |

Date |
Fri, 24 Jun 2005 10:03:12 -0500 |

Hans - This sounds like an ANOVA interaction. If you can get your data into "long" form, you can do an ANOVA with a command such as anova y fac1 fac2 fac1*fac2 where y is the dependent variable, fac1 is the first index of your group and fac2 is the second index. I looks as though your data is in "wide' form, so you probably have to "reshape" it. Al Feiveson -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Hans J. Baumgartner Sent: Friday, June 24, 2005 8:11 AM To: statalist@hsphsun2.harvard.edu Subject: st: difference-in-difference Dear statalist, I am trying to obtain the difference-in-difference estimator by using ttest. However, I got stocked somewhere half way. I ttested the difference in two groups. (see below). What I would like to do now is to check the difference of these two differences. Is there anyway to do this?` . ttest gruppe11 = gruppe10, unpaired Two-sample t test with equal variances ---------------------------------------------------------------------------- -- Variable | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------- ---------+------ gruppe11 | 36 .4444444 .0839921 .5039526 .2739314 .6149575 gruppe10 | 203 .4187192 .0347119 .4945689 .350275 .4871634 ---------+-------------------------------------------------------------- ---------+------ combined | 239 .4225941 .0320194 .4950087 .3595164 .4856719 ---------+-------------------------------------------------------------- ---------+------ diff | .0257252 .0896915 -.1509692 .2024197 ---------------------------------------------------------------------------- -- Degrees of freedom: 237 Ho: mean(gruppe11) - mean(gruppe10) = diff = 0 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 t = 0.2868 t = 0.2868 t = 0.2868 P < t = 0.6127 P > |t| = 0.7745 P > t = 0.3873 . ttest gruppe01 = gruppe00, unpaired Two-sample t test with equal variances ---------------------------------------------------------------------------- -- Variable | Obs Mean Std. Err. Std. Dev. [95% Conf. Interval] ---------+-------------------------------------------------------------- ---------+------ gruppe01 | 57 .7017544 .0611344 .4615545 .5792875 .8242213 gruppe00 | 285 .5017544 .0296694 .5008764 .4433546 .5601541 ---------+-------------------------------------------------------------- ---------+------ combined | 342 .5350877 .0270098 .4994981 .481961 .5882144 ---------+-------------------------------------------------------------- ---------+------ diff | .2 .0717663 .0588382 .3411618 ---------------------------------------------------------------------------- -- Degrees of freedom: 340 Ho: mean(gruppe01) - mean(gruppe00) = diff = 0 Ha: diff < 0 Ha: diff != 0 Ha: diff > 0 t = 2.7868 t = 2.7868 t = 2.7868 P < t = 0.9972 P > |t| = 0.0056 P > t = 0.0028 ++++++++++++++++++++++++++++++++ Hans J. Baumgartner Dept. Public Economics DIW Berlin German Institut for Economic Research phone: +49/30/89789-307 fax : +49/30/89789-114 URL: www.diw.de www.hansbaumgartner.de ++++++++++++++++++++++++++++++++ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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