Nick--
I don't think -duplicates- addresses the issue. The idea is, for
observation 1, find the k obs with the closest value of p (k a scalar,
say 4, and p a variable, measuring for example a propensity). Then
repeat for observation 2, but do not pick any of the obs you picked
for observation 1. Et cetera. "Duplicates" in this setting means
picking observations more than once, I believe.
This is presumably needed for some nonstandard form of propensity
score matching--on which see Rosenbaum and Rubin (1983), linked
directly from p.26 of http://pped.org/stata/ciwod.pdf
On Tue, Nov 18, 2008 at 2:17 PM, Nick Cox <[email protected]> wrote:
> At least part of this sounds very easy. If duplicates are not allowed,
> remove them first with -duplicates-.
>
> Nick
> [email protected]
>
> Gao Liu
>
> vmatch can match all observations based on certain criteria, like
> within some distance. However, what I want is the nearest N
> observations, where n is a fixed number. Also, duplicates are not
> allowed.
>
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