st: bootstrap with clustered data

["Litovitz, Aviva" <litovitz@prgs.edu>]

Statalist,

I am using the -bootstrap- command with clustered data in Stata 10 and I want to make sure I understand the role of -idcluster()-.

As a test of the -bootstrap- command, I am using an example I found in the archives (http://www.stata.com/statalist/archive/2006-11/msg00025.html):

	. webuse nlswork
	. bootstrap, seed(1234) cluster(idcode) idcluster(newid) : xtreg ln_w grade age*, i(newid) fe

If I understand correctly, -cluster(idcode)- sets the cluster variable and -idcluster(newid)- generates a new value for "newid" each time a cluster is sampled by the bootstrap.  Yet when I look at "newid" values after the bootstrap is complete, each cluster is numbered consecutively, as if there were no changes to "newid" during the bootstrap process.  Because "idcode" has some missing values, "newid" does not generally match "idcode".

Why do the values of "newid" not change in the dataset?

Thanks for any help!
Aviva



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