st: testing the difference between the estimated coefficients

["Sibel S." <sibsel08@gmail.com>]

If we run the following regressions,
regress a b if year==2005      *equation 1
regress a b if year==2000      *equation 2
how can one test the difference between the estimated coefficients (b
in equation 1 and b in equation 2) and get the t-statistic of
difference?Thanks.
*
*   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/