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Re: st: combining multiple strata with single psu


From   Steven Samuels <[email protected]>
To   [email protected]
Subject   Re: st: combining multiple strata with single psu
Date   Sat, 2 Jun 2007 10:38:38 -0400

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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