Using calipers in GenMatch to enourage more pairs

So following the example from the Matching package and in particular the GenMatch example

Link to package here

Following the example in GenMatch

library(Matching)

data(lalonde)
attach(lalonde)

X = cbind(age, educ, black, hisp, married, nodegr, u74, u75, re75, re74)

BalanceMat <- cbind(age, educ, black, hisp, married, nodegr, u74, u75, re75, re74,
                    I(re74*re75))

genout <- GenMatch(Tr=treat, X=X, BalanceMatrix=BalanceMat, estimand="ATE", M=1,
                   pop.size=16, max.generations=10, wait.generations=1)

genout$matches
genout$ecaliper

Y=re78/1000

mout <- Match(Y=Y, Tr=treat, X=X, Weight.matrix=genout)
summary(mout)

We see 185 treated observation are paired with 270 non-treatment observation. Now we want to relax this to allow for more flexible pairing on the age criteria.

We can generate a table with the teatment cases and their age on the left and the control case and age on the right by:

pairs <- data.frame(mout$index.treated, lalonde$age[mout$index.treated], mout$index.control, lalonde$age[mout$index.control])

Now using the caliper function of the Match() we should be able to generate a more relaxed match.

We see that sd(lalonde$age) gives us a SD of 7 years for our table, so lets try and match for this limit. Would one simply

mout2 <- Match(Y=Y, Tr=treat, X=X, Weight.matrix=genout, caliper=c(1,0,0,0,0,0,0,0,0,0))
summary(mout2)

it appear not because less Matched number of observations have occured in mout2 than mout1.

So where have I gone wrong? The values of zero must be included in caliper or else an error is returned if they are blank

Your first call to GenMatch did not impose any caliper. Your second call imposed a caliper so the number of matches will decrease. If you want to increase the number of matches in your first call, see the "M" option. You probably want something like 1-to-2 matching, etc.