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Re: st: combining multiple strata with single psu
My earlier answer assumed that all of Nora's strata were singletons,
and that was wrong. Still, my advice applies: Join a singleton
stratum to a "neighbor" or to one that is similar in other ways. If
the strata with adjacent numbers are "neighbors" then it is probably
easiest to create the new strata in Stata's Editor.
On Jun 1, 2007, at 3:21 PM, Steven Samuels wrote:
On Jun 1, 2007, at 2:16 PM, <[email protected]> wrote:
I suppose I was not quite clear enough before. I have svyset
the data, and actually know which strata are singletons,(list
strata psu if psu==1) the question I seem unable to solve is
how to take those singletons, together, and make them into a
new strata.
Combine "neighboring" strata so that you have n=2 in each new
stratum, no more if possible. (Having n=2 will facilitate using BRR
for variance estimation.) If you have an odd number of strata, the
last one will have n=3. There is a chance that the sequential
stratum numbers in your data set imply some geographic sequence If
not, number the strata in some other way so that neighboring strata
are close by. For geographic strata, one way is "serpentine"
numbering:
123
654
789
Then neighboring sequential strata can be combined by:
gen new_strat = int(stratum/2 + .5)
You might also have other information which allows you to group
similar strata into new ones. Beware of grouping on the basis of
similar "outcome" variables; this will induce artificially small
within-stratum SD.
-Steve
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