k2k {cem} | R Documentation |
Reduces a CEM output to a k2k matching
k2k(obj, data, method=NULL, mpower=2, verbose=0)
obj |
an object as output from cem |
data |
the original data.frame used by cem |
method |
distance method to use in k2k matching. See Details. |
mpower |
power of the Minkowski distance. See Details. |
verbose |
controls level of verbosity. Default=0. |
This function transforms a typical cem
matching solution
to a k
-to-k
match, with k
variable along strata:
i.e., in each stratum generated by cem
, the match is reduce to have
the same number of treated and control units. (This option will delete
some data that matched well, and thus likely increase the variance, but
it means that subsequent analyses do not require weights.)
The user can choose a method
(between `euclidean
',
`maximum
', `manhattan
', `canberra
', `binary
'
and `minkowski
') for nearest neighbor matching inside each
cem
strata. By default method
is set to `NULL
',
which means random matching inside cem
strata. For the Minkowski
distance the power can be specified via the argument mpower
'.
For more information on method != NULL
, refer to
dist
help page.
After k2k
the weights of each matched observation are set to unity.
obj |
an object of class cem.match |
Stefano Iacus, Gary King, and Giuseppe Porro
Stefano Iacus, Gary King, Giuseppe Porro, ``Matching for Casual Inference Without Balance Checking,'' http://gking.harvard.edu/files/abs/cem-abs.shtml
data(LL) # cem match: automatic bin choice mat <- cem(treatment="treated", data=LL, drop="re78") mat mat$k2k # ATT estimate att(mat, re78 ~ treated, data=LL) # transform the match into k2k mat2 <- k2k(mat, LL, "euclidean", 1) mat2 mat2$k2k # ATT estimate after k2k att(mat2, re78 ~ treated, data=LL)