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From | Maarten buis <maartenbuis@yahoo.co.uk> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: Estimating firm level data on regional level data using a within estimator. |
Date | Sun, 6 Jun 2010 04:56:36 -0700 (PDT) |
--- On Sun, 6/6/10, natasha agarwal wrote: > I estimate it with a within estimator, i.e. ur fixed > effects. When I do so the minute I include all the time > dummies, FDI goes insig but thats my main variable of > interest. The problem that I have found out is that FDI > is behaving like a time dummy because all the firms > within a region for each year will have the same value > of FDI. The problem with macro quantities is that they are usually highly correlated with other macro quantities and time, so it is hard to disentangle the effects. Moreover, there are only so many observations possible on the macro level. These two together means that often you have very little statistical power to play with. The advantage of fixed effects regression is that it provides a strong reason for believing that you controlled for some of the unobserved and possible confounding variables on the the region level. However, the price you have to pay is that you loose a lot of power; i.e. you loose all the information from the comparison between regions. Since you don't have a lot to begin with, that is very bad news. Random effects don't allow you to controll for unobserved confounding variables on the region level (the random effects are assumed to be uncorrelated with the observed variables), but it does allow you to also use the information from the comparison between regions. Then you have rather pragmatic discipline specific reasons: e.g. within economics they tend to be so obsessed with fixed effects regression, that you will have a hard time getting a random effects model published. Hope this helps, Maarten -------------------------- Maarten L. Buis Institut fuer Soziologie Universitaet Tuebingen Wilhelmstrasse 36 72074 Tuebingen Germany http://www.maartenbuis.nl -------------------------- * * 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/