st: IVREG2 and Standard Errors when Number of Clusters is Small

[Jessie C <jessiecoh@gmail.com>]

I am running a cross-country type regression using ivreg2.  The amount
of clusters is less than 42.  For example, you can think of the unit
of observation as country and the cluster as continent.  Though it is
a slightly different context and I have 12 clusters.  How exactly
should standard errors be adjusted?
*
*   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/