Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
From | Clive Nicholas <clivelists@googlemail.com> |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: fixed vs random effect model |
Date | Sun, 4 Jul 2010 21:34:15 +0100 |
Martin Weiss replied to Amatoallah Ouchen: > The assumptions underlying the RE model are rarely fulfilled. To choose the > model based on the pleasant answers that it gives you would be a problem for > the referee, I guess. You must sell your choice differently... Quite right: it's never been fulfilled in my experience; so much so that I never bother fitting random-effects models anymore unless the correlation between the fixed effects and the RHS covariates is zero (or very nearly). In addition to Hausman tests, you can check this quite easily when running, say, FE models using -xtreg, fe-, so why haven't you? . webuse grunfeld . xtset company year panel variable: company (strongly balanced) time variable: year, 1935 to 1954 . xtreg invest mvalue kstock, i(company) fe Fixed-effects (within) regression Number of obs = 200 Group variable (i): company Number of groups = 10 R-sq: within = 0.7668 Obs per group: min = 20 between = 0.8194 avg = 20.0 overall = 0.8060 max = 20 F(2,188) = 309.01 corr(u_i, Xb) = -0.1517 Prob > F = 0.0000 ^^^^^^^^^^^^^^^^^^^^^^^^^^ ------------------------------------------------------------------------------ invest | Coef. Std. Err. t P>|t| [95% Conf. Interval] -------------+---------------------------------------------------------------- mvalue | .1101238 .0118567 9.29 0.000 .0867345 .1335131 kstock | .3100653 .0173545 17.87 0.000 .2758308 .3442999 _cons | -58.74393 12.45369 -4.72 0.000 -83.31086 -34.177 -------------+---------------------------------------------------------------- sigma_u | 85.732501 sigma_e | 52.767964 rho | .72525012 (fraction of variance due to u_i) ------------------------------------------------------------------------------ F test that all u_i=0: F(9, 188) = 49.18 Prob > F = 0.0000 -- Clive Nicholas [Please DO NOT mail me personally here, but at <clivenicholas@hotmail.com>. Please respond to contributions I make in a list thread here. Thanks!] "My colleagues in the social sciences talk a great deal about methodology. I prefer to call it style." -- Freeman J. Dyson. * * 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/