ERROR: A feasible optimal fixed ratio matching that has the specified parameters does not exist. I meet this problem when I do the 1-5 optimal matching, here is the code: /* Perform the 1-to-5 optimal matching */
proc psmatch data=DRUGS region=allobs;
class Treatment Gender;
psmodel Treatment(Treated='1') = Gender Age BMI;
match method=optimal(k=5) exact=Gender distance=ps caliper=0.5;
output out(obs=match)=matched2 matchid=_MatchID;
run; If I change the k=1, it could run, while it showed error when I put k=5.
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