Hi everyone,

I am trying to perform a 1:4 propensity score matching using the command psmatch2. After I run the code, the ratio of individuals in the treatment group to the individuals in the control group is approximately equal to 1:4 (23.6% and 76.4% instead of 25% and 75%). Whenever a 1:n matching is reported in the literature, the number of individuals matched is always exactly equal to the pre-specified ratio. Here's my code:

Code:
psmatch2 group, neighbor(4) pscore(score) caliper (0.2) quietly

*Creating matching groups
gen pair1 = _id if _treated==0
replace pair1 = _n1 if _treated==1

gen pair2 = _id if _treated==0
replace pair2 = _n2 if _treated==1

gen pair3 = _id if _treated==0
replace pair3 = _n3 if _treated==1

gen pair4 = _id if _treated==0
replace pair4 = _n4 if _treated==1

bysort pair1: egen paircount1 = count(pair1)
bysort pair2: egen paircount2 = count(pair2)
bysort pair3: egen paircount3 = count(pair3)
bysort pair4: egen paircount4 = count(pair4)

egen byte paircount = anycount(paircount1 paircount2 paircount3 paircount4), values(2)

tab group if paircount!=0

HTML Code:
group    Freq.    Percent    Cum.
            
0    1,248    76.38    76.38
1    386    23.62    100.00
            
Total    1,634    100.00

Am I doing something wrong? How can I arrive to a ratio of 25% to 75%?

Thanks