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st: "cluster(): too many variables" in ivreg2 despite latest version?

From   Jen Zhen <>
Subject   st: "cluster(): too many variables" in ivreg2 despite latest version?
Date   Thu, 17 Oct 2013 14:00:32 +0200

Dear listers,

(1) When specifying two-dimensional clustering in -ivreg2-,
ivreg2 depvar controlvar (endogreg = instrument), cluster(dimension1
I always get the error "cluster(): Too many variables specified".

Many earlier posts on the topic on Statalist suggest that this problem
should be solved by ensuring to have at least the 2010 version of
-ivreg2-. While my Stata cannot be updated automatically, I have
downloaded 2013 versions of both ivreg2 and of ranktest, and I have
also checked -which ivreg2, all- that I currently have only that 1
version of the ado file in my PLUS ado file path. Nonetheless the
problem persists. Would anyone know what else I could try? Does ivreg2
maybe require any other ado files that might also need manual

(2) Nichols 2007 recommends to have at least 50 different clusters and
Angrist & Pischke similarly suggests to have at least 42. So I'm
taking this into account when choosing on which dimensions to cluster
my standard errors. What I'm wondering though is: Should I also make
sure to have no or few clusters with fewer than ... observations? In
particular, with the way I am currently clustering, I have a few
clusters with just 2 observations, although 95% of my clusters have
more than 17. With 2 way clustering, any such requirement would
presumably need to be independently satisfied for each of my 2

Thank you so much and kind regards, JZ
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