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| From | Stas Kolenikov <skolenik@gmail.com> |
| To | statalist@hsphsun2.harvard.edu |
| Subject | Re: st: Difference-in-Difference with N=4, missing std. errors |
| Date | Sun, 5 Dec 2010 10:37:33 -0600 |
That's a theory of linear models issue: you have 4 equations with 4 unknowns, so you consume all information in the sample; you don't have any degrees of freedom to estimate variance of the error term in the regression, and hence end up with no standard errors or F-tests. On Sun, Dec 5, 2010 at 10:10 AM, Jennifer Maki <jenanneharris@hotmail.com> wrote: > > Statalist:I'm trying to use difference in differences to tease out the effect of a policy change. I'm using country level data and have yearly figures for both countries. I averaged them so that I have a figure representing the 5-year average pre & post treatment for both countries. leaving me with 4 observations. When I estimate this using the regress command in Stata, the coefficient on the interaction term is what I get when I calculate the difference in difference by hand, but I don't get standard errors or p-values in the output. Is there a way to get this information so that I can present the statistical significance of my findings? > Thanks you,Jen > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > -- Stas Kolenikov, also found at http://stas.kolenikov.name Small print: I use this email account for mailing lists only. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/