RE: st: RE: nnmatch error in PSM

[Joe Canner <jcanner1@jhmi.edu>]

Yes, there are a number of options that can be specified regarding the matching method, case:control ratio, caliper, etc.  The -noreplacement- option is what you want.

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Katherine Picho
Sent: Wednesday, September 11, 2013 11:47 AM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: RE: nnmatch error in PSM

I will try this out and let you know how it goes. Are you able to match without replacement  using psmatch2 (Im assuming yes!)

On Wed, Sep 11, 2013 at 10:34 AM, Joe Canner <jcanner1@jhmi.edu> wrote:
> Katherine,
>
> I don't have much experience with -nnmatch- but I have had good success with -psmatch2-, which generates the propensity scores and does the matching all in one step.  It seems to be a little more robust and efficient than the -pscore-/-nnmatch- combination.
>
> Regards,
> Joe Canner
> Johns Hopkins University School of Medicine
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu 
> [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Katherine 
> Picho
> Sent: Wednesday, September 11, 2013 10:25 AM
> To: statalist@hsphsun2.harvard.edu
> Subject: st: nnmatch error in PSM
>
> Hi all
>
> I'm currently attempting propensity score matching with nearest neighbor using the nnmatch.
>
> However, at some point in running my ado file, STATA returns an error
> message: "Insufficient memory to create more variables:Either increase memory or decrease m"
>
>  I only have about 290 variables in the current dataset (21k observations).
>  I'm only matching using 3 variables. I'm using STATA IC and the max # var is 2048 (which is way more that I could ever use for this specific purpose).
>
> Even when I reduce the dataset to only 40 variables, and still match on the 3 variables of interest, the problem/ error code remains the same.
> I have 3615 treatment observations that I'd like to match from a pool 
> of about 16,500 controls (so theoretically this should not be a
> problem)
> My matching variables are categorical
>
> the nnmatch command that I run (where I run into trouble) is:
>
> nnmatch Depvar trtmt pscore, tc(att) m(1) keep(matched_att) replace
>
> this is where it generates the error message.
>
> I tried to remedy potential memory problems like- compressing the 
> data/ variables. expanding the memory. (help query, within stata 
> itself), etc, Nothing works. A search on the statalist archives 
> indicates that a few people have run into the same problems using
> nnmatch-- but none of the queries I found had received any responses on how to fix the problem.
>
> If anyone here has run into a similar issue that they were able to fix, please let me know. Thanks!
>
> Katherine
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