Hi,

I am using Coursened Exact Matching to improve balance in my sample. The summary matching results after applying CEM are that 11,128 pixels have been matched:

Sample sizes:
          Control Treated
All         19741    8283
Matched      6728    4400
Unmatched   13013    3883
Discarded       0       0

Firstly, is it possible to specify 1:1 matching with CEM? I want to only retain matched pairs, which requires the same amount of pixels in my treatment & control groups.

I am also having trouble getting a unique identifier for each matched pair so that I can calculate the difference between the treatment and control. I am using the code:

pair: Produces a paired sample out of a CEM match solution 

When I execute the below command, it says there are 0 matches.

> # we want a set of paired units
> pairsample <- pair(match.out_cem, data)
 
Total number of units paired in CEM strata: 0
Total number of units matched: 0

Can anyone help or point me in the right direction?

Thanks, Tori

Victoria Graham | MPhil., PhD candidate
Macquarie University NSW 2109 Australia
T: +61 2 9850 6298 | E: victoria.graham@mq.edu.au
Twitter:@ToriFGraham