`matchit()`

is the main function of *MatchIt* and performs
pairing, subset selection, and subclassification with the aim of creating
treatment and control groups balanced on included covariates. *MatchIt*
implements the suggestions of Ho, Imai, King, and Stuart (2007) for
improving parametric statistical models by preprocessing data with
nonparametric matching methods.

This page documents the overall use of `matchit()`

, but for specifics
of how `matchit()`

works with individual matching methods, see the
individual pages linked in the Details section below.

```
matchit(
formula,
data = NULL,
method = "nearest",
distance = "glm",
link = "logit",
distance.options = list(),
estimand = "ATT",
exact = NULL,
mahvars = NULL,
antiexact = NULL,
discard = "none",
reestimate = FALSE,
s.weights = NULL,
replace = FALSE,
m.order = NULL,
caliper = NULL,
std.caliper = TRUE,
ratio = 1,
verbose = FALSE,
include.obj = FALSE,
...
)
# S3 method for matchit
print(x, ...)
```

- formula
a two-sided

`formula`

object containing the treatment and covariates to be used in creating the distance measure used in the matching. This formula will be supplied to the functions that estimate the distance measure. The formula should be specified as`A ~ X1 + X2 + ...`

where`A`

represents the treatment variable and`X1`

and`X2`

are covariates.- data
a data frame containing the variables named in

`formula`

and possible other arguments. If not found in`data`

, the variables will be sought in the environment.- method
the matching method to be used. The allowed methods are

`"nearest"`

for nearest neighbor matching (on the propensity score by default),`"optimal"`

for optimal pair matching,`"full"`

for optimal full matching,`"genetic"`

for genetic matching,`"cem"`

for coarsened exact matching,`"exact"`

for exact matching,`"cardinality"`

for cardinality and template matching, and`"subclass"`

for subclassification. When set to`NULL`

, no matching will occur, but propensity score estimation and common support restrictions will still occur if requested. See the linked pages for each method for more details on what these methods do, how the arguments below are used by each on, and what additional arguments are allowed.- distance
the distance measure to be used. Can be either the name of a method of estimating propensity scores (e.g.,

`"glm"`

), the name of a method of computing a distance matrix from the covariates (e.g.,`"mahalanobis"`

), a vector of already-computed distance measures, or a matrix of pairwise distances. See`distance`

for allowable options. The default is`"glm"`

for propensity scores estimated with logistic regression using`glm()`

. Ignored for some methods; see individual methods pages for information on whether and how the distance measure is used.- link
when

`distance`

is specified as a string, an additional argument controlling the link function used in estimating the distance measure. Allowable options depend on the specific`distance`

value specified. See`distance`

for allowable options with each option. The default is`"logit"`

, which, along with`distance = "glm"`

, identifies the default measure as logistic regression propensity scores.- distance.options
a named list containing additional arguments supplied to the function that estimates the distance measure as determined by the argument to

`distance`

. See distance for an example of its use.- estimand
a string containing the name of the target estimand desired. Can be one of

`"ATT"`

or`"ATC"`

. Some methods accept`"ATE"`

as well. Default is`"ATT"`

. See Details and the individual methods pages for information on how this argument is used.- exact
for methods that allow it, for which variables exact matching should take place. Can be specified as a string containing the names of variables in

`data`

to be used or a one-sided formula with the desired variables on the right-hand side (e.g.,`~ X3 + X4`

). See the individual methods pages for information on whether and how this argument is used.- mahvars
for methods that allow it, on which variables Mahalanobis distance matching should take place when

`distance`

corresponds to propensity scores. Usually used to perform Mahalanobis distance matching within propensity score calipers, where the propensity scores are computed using`formula`

and`distance`

. Can be specified as a string containing the names of variables in`data`

to be used or a one-sided formula with the desired variables on the right-hand side (e.g.,`~ X3 + X4`

). See the individual methods pages for information on whether and how this argument is used.- antiexact
for methods that allow it, for which variables anti-exact matching should take place. Anti-exact matching ensures paired individuals do not have the same value of the anti-exact matching variable(s). Can be specified as a string containing the names of variables in

`data`

to be used or a one-sided formula with the desired variables on the right-hand side (e.g.,`~ X3 + X4`

). See the individual methods pages for information on whether and how this argument is used.- discard
a string containing a method for discarding units outside a region of common support. When a propensity score is estimated or supplied to

`distance`

as a vector, the options are`"none"`

,`"treated"`

,`"control"`

, or`"both"`

. For`"none"`

, no units are discarded for common support. Otherwise, units whose propensity scores fall outside the corresponding region are discarded. Can also be a`logical`

vector where`TRUE`

indicates the unit is to be discarded. Default is`"none"`

for no common support restriction. See Details.- reestimate
if

`discard`

is not`"none"`

and propensity scores are estimated, whether to re-estimate the propensity scores in the remaining sample. Default is`FALSE`

to use the propensity scores estimated in the original sample.- s.weights
an optional numeric vector of sampling weights to be incorporated into propensity score models and balance statistics. Can also be specified as a string containing the name of variable in

`data`

to be used or a one-sided formula with the variable on the right-hand side (e.g.,`~ SW`

). Not all propensity score models accept sampling weights; see distance for information on which do and do not, and see`vignette("sampling-weights")`

for details on how to use sampling weights in a matching analysis.- replace
for methods that allow it, whether matching should be done with replacement (

`TRUE`

), where control units are allowed to be matched to several treated units, or without replacement (`FALSE`

), where control units can only be matched to one treated unit each. See the individual methods pages for information on whether and how this argument is used. Default is`FALSE`

for matching without replacement.- m.order
for methods that allow it, the order that the matching takes place. Allowable options depend on the matching method but include

`"largest"`

, where matching takes place in descending order of distance measures;`"smallest"`

, where matching takes place in ascending order of distance measures;`"random"`

, where matching takes place in a random order; and`"data"`

where matching takes place based on the order of units in the data. When`m.order = "random"`

, results may differ across different runs of the same code unless a seed is set and specified with`set.seed()`

. See the individual methods pages for information on whether and how this argument is used. The default of`NULL`

corresponds to`"largest"`

when a propensity score is estimated or supplied as a vector and`"data"`

otherwise.- caliper
for methods that allow it, the width(s) of the caliper(s) to use in matching. Should be a numeric vector with each value named according to the variable to which the caliper applies. To apply to the distance measure, the value should be unnamed. See the individual methods pages for information on whether and how this argument is used. The default is

`NULL`

for no caliper.- std.caliper
`logical`

; when a caliper is specified, whether the the caliper is in standard deviation units (`TRUE`

) or raw units (`FALSE`

). Can either be of length 1, applying to all calipers, or of length equal to the length of`caliper`

. Default is`TRUE`

.- ratio
for methods that allow it, how many control units should be matched to each treated unit in k:1 matching. Should be a single integer value. See the individual methods pages for information on whether and how this argument is used. The default is 1 for 1:1 matching.

- verbose
`logical`

; whether information about the matching process should be printed to the console. What is printed depends on the matching method. Default is`FALSE`

for no printing other than warnings.- include.obj
`logical`

; whether to include any objects created in the matching process in the output, i.e., by the functions from other packages`matchit()`

calls. What is included depends on the matching method. Default is`FALSE`

.- ...
additional arguments passed to the functions used in the matching process. See the individual methods pages for information on what additional arguments are allowed for each method. Ignored for

`print()`

.- x
a

`matchit`

object.

When `method`

is something other than `"subclass"`

, a
`matchit`

object with the following components:

- match.matrix
a matrix containing the matches. The rownames correspond to the treated units and the values in each row are the names (or indices) of the control units matched to each treated unit. When treated units are matched to different numbers of control units (e.g., with exact matching or matching with a caliper), empty spaces will be filled with

`NA`

. Not included when`method`

is`"full"`

,`"cem"`

(unless`k2k = TRUE`

),`"exact"`

, or`"cardinality"`

.- subclass
a factor containing matching pair/stratum membership for each unit. Unmatched units will have a value of

`NA`

. Not included when`replace = TRUE`

.- weights
a numeric vector of estimated matching weights. Unmatched and discarded units will have a weight of zero.

- model
the fit object of the model used to estimate propensity scores when

`distance`

is specified and not`"mahalanobis"`

or a numeric vector. When`reestimate = TRUE`

, this is the model estimated after discarding units.- X
a data frame of covariates mentioned in

`formula`

,`exact`

,`mahvars`

, and`antiexact`

.- call
the

`matchit()`

call.- info
information on the matching method and distance measures used.

- estimand
the argument supplied to

`estimand`

.- formula
the

`formula`

supplied.- treat
a vector of treatment status converted to zeros (0) and ones (1) if not already in that format.

- distance
a vector of distance values (i.e., propensity scores) when

`distance`

is supplied as a method of estimating propensity scores or a numeric vector.- discarded
a logical vector denoting whether each observation was discarded (

`TRUE`

) or not (`FALSE`

) by the argument to`discard`

.- s.weights
the vector of sampling weights supplied to the

`s.weights`

argument, if any.- exact
a one-sided formula containing the variables, if any, supplied to

`exact`

.- mahvars
a one-sided formula containing the variables, if any, supplied to

`mahvars`

.- obj
when

`include.obj = TRUE`

, an object containing the intermediate results of the matching procedure. See the individual methods pages for what this component will contain.

When `method = "subclass"`

, a `matchit.subclass`

object with the same
components as above except that `match.matrix`

is excluded and one
additional component, `q.cut`

, is included, containing a vector of the
distance measure cutpoints used to define the subclasses. See
`method_subclass`

for details.

Details for the various matching methods can be found at the following help pages:

`method_nearest`

for nearest neighbor matching`method_optimal`

for optimal pair matching`method_full`

for optimal full matching`method_genetic`

for genetic matching`method_cem`

for coarsened exact matching`method_exact`

for exact matching`method_cardinality`

for cardinality and template matching`method_subclass`

for subclassification

The pages contain information on what the method does, which of the arguments above are
allowed with them and how they are interpreted, and what additional
arguments can be supplied to further tune the method. Note that the default
method with no arguments supplied other than `formula`

and `data`

is 1:1 nearest neighbor matching without replacement on a propensity score
estimated using a logistic regression of the treatment on the covariates.
This is not the same default offered by other matching programs, such as
those in *Matching*, `teffects`

in Stata, or `PROC PSMATCH`

in SAS, so care should be taken if trying to replicate the results of those
programs.

When `method = NULL`

, no matching will occur, but any propensity score
estimation and common support restriction will. This can be a simple way to
estimate the propensity score for use in future matching specifications
without having to re-estimate it each time. The `matchit()`

output with
no matching can be supplied to `summary()`

to examine balance prior to
matching on any of the included covariates and on the propensity score if
specified. All arguments other than `distance`

, `discard`

, and
`reestimate`

will be ignored.

See distance for details on the several ways to
specify the `distance`

, `link`

, and `distance.options`

arguments to estimate propensity scores and create distance measures.

When the treatment variable is not a `0/1`

variable, it will be coerced
to one and returned as such in the `matchit()`

output (see section
Value, below). The following rules are used: 1) if `0`

is one of the
values, it will be considered the control and the other value the treated;
2) otherwise, if the variable is a factor, `levels(treat)[1]`

will be
considered control and the other variable the treated; 3) otherwise,
`sort(unique(treat))[1]`

will be considered control and the other value
the treated. It is safest to ensure the treatment variable is a `0/1`

variable.

The `discard`

option implements a common support restriction. It can
only be used when a distance measure is an estimated propensity score or supplied as a vector and is ignored for some matching
methods. When specified as `"treated"`

, treated units whose distance
measure is outside the range of distance measures of the control units will
be discarded. When specified as `"control"`

, control units whose
distance measure is outside the range of distance measures of the treated
units will be discarded. When specified as `"both"`

, treated and
control units whose distance measure is outside the intersection of the
range of distance measures of the treated units and the range of distance
measures of the control units will be discarded. When `reestimate = TRUE`

and `distance`

corresponds to a propensity score-estimating
function, the propensity scores are re-estimated in the remaining units
prior to being used for matching or calipers.

Caution should be used when interpreting effects estimated with various
values of `estimand`

. Setting `estimand = "ATT"`

doesn't
necessarily mean the average treatment effect in the treated is being
estimated; it just means that for matching methods, treated units will be
untouched and given weights of 1 and control units will be matched to them
(and the opposite for `estimand = "ATC"`

). If a caliper is supplied or
treated units are removed for common support or some other reason (e.g.,
lacking matches when using exact matching), the actual estimand targeted is
not the ATT but the treatment effect in the matched sample. The argument to
`estimand`

simply triggers which units are matched to which, and for
stratification-based methods (exact matching, CEM, full matching, and
subclassification), determines the formula used to compute the
stratification weights.

Matching weights are computed in one of two ways depending on whether matching was done with replacement or not.

For matching *without* replacement (except for cardinality matching), each
unit is assigned to a subclass, which represents the pair they are a part of
(in the case of k:1 matching) or the stratum they belong to (in the case of
exact matching, coarsened exact matching, full matching, or
subclassification). The formula for computing the weights depends on the
argument supplied to `estimand`

. A new stratum "propensity score"
(`p`

) is computed as the proportion of units in each stratum that are
in the treated group, and all units in that stratum are assigned that
propensity score. Weights are then computed using the standard formulas for
inverse probability weights: for the ATT, weights are 1 for the treated
units and `p/(1-p)`

for the control units; for the ATC, weights are
`(1-p)/p`

for the treated units and 1 for the control units; for the
ATE, weights are `1/p`

for the treated units and `1/(1-p)`

for the
control units. For cardinality matching, all matched units receive a weight
of 1.

For matching *with* replacement, units are not assigned to unique strata. For
the ATT, each treated unit gets a weight of 1. Each control unit is weighted
as the sum of the inverse of the number of control units matched to the same
treated unit across its matches. For example, if a control unit was matched
to a treated unit that had two other control units matched to it, and that
same control was matched to a treated unit that had one other control unit
matched to it, the control unit in question would get a weight of 1/3 + 1/2
= 5/6. For the ATC, the same is true with the treated and control labels
switched. The weights are computed using the `match.matrix`

component
of the `matchit()`

output object.

In each treatment group, weights are divided by the mean of the nonzero
weights in that treatment group to make the weights sum to the number of
units in that treatment group. If sampling weights are included through the
`s.weights`

argument, they will be included in the `matchit()`

output object but not incorporated into the matching weights.
`match.data()`

, which extracts the matched set from a `matchit`

object,
combines the matching weights and sampling weights.

Ho, D. E., Imai, K., King, G., & Stuart, E. A. (2007). Matching
as Nonparametric Preprocessing for Reducing Model Dependence in Parametric
Causal Inference. *Political Analysis*, 15(3), 199–236. doi:10.1093/pan/mpl013

Ho, D. E., Imai, K., King, G., & Stuart, E. A. (2011). MatchIt:
Nonparametric Preprocessing for Parametric Causal Inference. *Journal of
Statistical Software*, 42(8). doi:10.18637/jss.v042.i08

`summary.matchit()`

for balance assessment after matching, `plot.matchit()`

for plots of covariate balance and propensity score overlap after matching.

`vignette("MatchIt")`

for an introduction to matching with
*MatchIt*; `vignette("matching-methods")`

for descriptions of the
variety of matching methods and options available;
`vignette("assessing-balance")`

for information on assessing the
quality of a matching specification; `vignette("estimating-effects")`

for instructions on how to estimate treatment effects after matching; and
`vignette("sampling-weights")`

for a guide to using *MatchIt* with
sampling weights.

```
data("lalonde")
# Default: 1:1 NN PS matching w/o replacement
m.out1 <- matchit(treat ~ age + educ + race + nodegree +
married + re74 + re75, data = lalonde)
m.out1
#> A matchit object
#> - method: 1:1 nearest neighbor matching without replacement
#> - distance: Propensity score
#> - estimated with logistic regression
#> - number of obs.: 614 (original), 370 (matched)
#> - target estimand: ATT
#> - covariates: age, educ, race, nodegree, married, re74, re75
summary(m.out1)
#>
#> Call:
#> matchit(formula = treat ~ age + educ + race + nodegree + married +
#> re74 + re75, data = lalonde)
#>
#> Summary of Balance for All Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5774 0.1822 1.7941 0.9211 0.3774
#> age 25.8162 28.0303 -0.3094 0.4400 0.0813
#> educ 10.3459 10.2354 0.0550 0.4959 0.0347
#> raceblack 0.8432 0.2028 1.7615 . 0.6404
#> racehispan 0.0595 0.1422 -0.3498 . 0.0827
#> racewhite 0.0973 0.6550 -1.8819 . 0.5577
#> nodegree 0.7081 0.5967 0.2450 . 0.1114
#> married 0.1892 0.5128 -0.8263 . 0.3236
#> re74 2095.5737 5619.2365 -0.7211 0.5181 0.2248
#> re75 1532.0553 2466.4844 -0.2903 0.9563 0.1342
#> eCDF Max
#> distance 0.6444
#> age 0.1577
#> educ 0.1114
#> raceblack 0.6404
#> racehispan 0.0827
#> racewhite 0.5577
#> nodegree 0.1114
#> married 0.3236
#> re74 0.4470
#> re75 0.2876
#>
#> Summary of Balance for Matched Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5774 0.3629 0.9740 0.7564 0.1321
#> age 25.8162 25.2054 0.0854 0.4633 0.0839
#> educ 10.3459 10.5838 -0.1183 0.5862 0.0222
#> raceblack 0.8432 0.4703 1.0259 . 0.3730
#> racehispan 0.0595 0.2108 -0.6400 . 0.1514
#> racewhite 0.0973 0.3189 -0.7478 . 0.2216
#> nodegree 0.7081 0.6486 0.1308 . 0.0595
#> married 0.1892 0.2000 -0.0276 . 0.0108
#> re74 2095.5737 2476.9475 -0.0780 1.2629 0.0546
#> re75 1532.0553 1669.7419 -0.0428 1.4712 0.0508
#> eCDF Max Std. Pair Dist.
#> distance 0.4216 0.9740
#> age 0.2541 1.3893
#> educ 0.0649 1.2205
#> raceblack 0.3730 1.0259
#> racehispan 0.1514 1.0514
#> racewhite 0.2216 0.8208
#> nodegree 0.0595 0.9868
#> married 0.0108 0.8005
#> re74 0.2865 0.8160
#> re75 0.2108 0.7552
#>
#> Sample Sizes:
#> Control Treated
#> All 429 185
#> Matched 185 185
#> Unmatched 244 0
#> Discarded 0 0
#>
# 1:1 NN Mahalanobis distance matching w/ replacement and
# exact matching on married and race
m.out2 <- matchit(treat ~ age + educ + race + nodegree +
married + re74 + re75, data = lalonde,
distance = "mahalanobis", replace = TRUE,
exact = ~ married + race)
m.out2
#> A matchit object
#> - method: 1:1 nearest neighbor matching with replacement
#> - distance: Mahalanobis
#> - number of obs.: 614 (original), 262 (matched)
#> - target estimand: ATT
#> - covariates: age, educ, race, nodegree, married, re74, re75
summary(m.out2, un = TRUE)
#>
#> Call:
#> matchit(formula = treat ~ age + educ + race + nodegree + married +
#> re74 + re75, data = lalonde, distance = "mahalanobis", exact = ~married +
#> race, replace = TRUE)
#>
#> Summary of Balance for All Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> age 25.8162 28.0303 -0.3094 0.4400 0.0813
#> educ 10.3459 10.2354 0.0550 0.4959 0.0347
#> raceblack 0.8432 0.2028 1.7615 . 0.6404
#> racehispan 0.0595 0.1422 -0.3498 . 0.0827
#> racewhite 0.0973 0.6550 -1.8819 . 0.5577
#> nodegree 0.7081 0.5967 0.2450 . 0.1114
#> married 0.1892 0.5128 -0.8263 . 0.3236
#> re74 2095.5737 5619.2365 -0.7211 0.5181 0.2248
#> re75 1532.0553 2466.4844 -0.2903 0.9563 0.1342
#> eCDF Max
#> age 0.1577
#> educ 0.1114
#> raceblack 0.6404
#> racehispan 0.0827
#> racewhite 0.5577
#> nodegree 0.1114
#> married 0.3236
#> re74 0.4470
#> re75 0.2876
#>
#> Summary of Balance for Matched Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> age 25.8162 25.6162 0.0280 0.6506 0.0466
#> educ 10.3459 10.3946 -0.0242 1.1552 0.0065
#> raceblack 0.8432 0.8432 0.0000 . 0.0000
#> racehispan 0.0595 0.0595 0.0000 . 0.0000
#> racewhite 0.0973 0.0973 0.0000 . 0.0000
#> nodegree 0.7081 0.7135 -0.0119 . 0.0054
#> married 0.1892 0.1892 0.0000 . 0.0000
#> re74 2095.5737 1861.6424 0.0479 1.4962 0.0286
#> re75 1532.0553 1091.6516 0.1368 2.0313 0.0347
#> eCDF Max Std. Pair Dist.
#> age 0.1784 0.4918
#> educ 0.0324 0.2070
#> raceblack 0.0000 0.0000
#> racehispan 0.0000 0.0000
#> racewhite 0.0000 0.0000
#> nodegree 0.0054 0.0119
#> married 0.0000 0.0000
#> re74 0.1784 0.2606
#> re75 0.0811 0.2445
#>
#> Sample Sizes:
#> Control Treated
#> All 429. 185
#> Matched (ESS) 33.65 185
#> Matched 77. 185
#> Unmatched 352. 0
#> Discarded 0. 0
#>
# 2:1 NN Mahalanobis distance matching within caliper defined
# by a probit pregression PS
m.out3 <- matchit(treat ~ age + educ + race + nodegree +
married + re74 + re75, data = lalonde,
distance = "glm", link = "probit",
mahvars = ~ age + educ + re74 + re75,
caliper = .1, ratio = 2)
m.out3
#> A matchit object
#> - method: 2:1 nearest neighbor matching without replacement
#> - distance: Mahalanobis [matching]
#> Propensity score [caliper]
#> - estimated with probit regression
#> - caliper: <distance> (0.029)
#> - number of obs.: 614 (original), 257 (matched)
#> - target estimand: ATT
#> - covariates: age, educ, race, nodegree, married, re74, re75
summary(m.out3, un = TRUE)
#>
#> Call:
#> matchit(formula = treat ~ age + educ + race + nodegree + married +
#> re74 + re75, data = lalonde, distance = "glm", link = "probit",
#> mahvars = ~age + educ + re74 + re75, caliper = 0.1, ratio = 2)
#>
#> Summary of Balance for All Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5773 0.1817 1.8276 0.8777 0.3774
#> age 25.8162 28.0303 -0.3094 0.4400 0.0813
#> educ 10.3459 10.2354 0.0550 0.4959 0.0347
#> raceblack 0.8432 0.2028 1.7615 . 0.6404
#> racehispan 0.0595 0.1422 -0.3498 . 0.0827
#> racewhite 0.0973 0.6550 -1.8819 . 0.5577
#> nodegree 0.7081 0.5967 0.2450 . 0.1114
#> married 0.1892 0.5128 -0.8263 . 0.3236
#> re74 2095.5737 5619.2365 -0.7211 0.5181 0.2248
#> re75 1532.0553 2466.4844 -0.2903 0.9563 0.1342
#> eCDF Max
#> distance 0.6413
#> age 0.1577
#> educ 0.1114
#> raceblack 0.6404
#> racehispan 0.0827
#> racewhite 0.5577
#> nodegree 0.1114
#> married 0.3236
#> re74 0.4470
#> re75 0.2876
#>
#> Summary of Balance for Matched Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5113 0.4932 0.0835 1.0778 0.0253
#> age 26.0721 24.9459 0.1574 0.4310 0.0928
#> educ 10.4144 10.3514 0.0314 0.6279 0.0171
#> raceblack 0.7387 0.7252 0.0372 . 0.0135
#> racehispan 0.0991 0.0946 0.0190 . 0.0045
#> racewhite 0.1622 0.1802 -0.0608 . 0.0180
#> nodegree 0.6667 0.6396 0.0594 . 0.0270
#> married 0.1892 0.2297 -0.1035 . 0.0405
#> re74 3016.7936 2280.7013 0.1506 1.8738 0.0569
#> re75 2023.1731 1525.9838 0.1544 2.0215 0.0434
#> eCDF Max Std. Pair Dist.
#> distance 0.1441 0.0860
#> age 0.3198 0.9487
#> educ 0.0586 0.7324
#> raceblack 0.0135 0.0565
#> racehispan 0.0045 0.4924
#> racewhite 0.0180 0.3236
#> nodegree 0.0270 0.5725
#> married 0.0405 0.4722
#> re74 0.2117 0.5502
#> re75 0.1081 0.5885
#>
#> Sample Sizes:
#> Control Treated
#> All 429. 185
#> Matched (ESS) 131.78 111
#> Matched 146. 111
#> Unmatched 283. 74
#> Discarded 0. 0
#>
# Optimal full PS matching for the ATE within calipers on
# PS, age, and educ
m.out4 <- matchit(treat ~ age + educ + race + nodegree +
married + re74 + re75, data = lalonde,
method = "full", estimand = "ATE",
caliper = c(.1, age = 2, educ = 1),
std.caliper = c(TRUE, FALSE, FALSE))
m.out4
#> A matchit object
#> - method: Optimal full matching
#> - distance: Propensity score [caliper]
#> - estimated with logistic regression
#> - caliper: <distance> (0.029), age (2), educ (1)
#> - number of obs.: 614 (original), 314 (matched)
#> - target estimand: ATE
#> - covariates: age, educ, race, nodegree, married, re74, re75
summary(m.out4, un = TRUE)
#>
#> Call:
#> matchit(formula = treat ~ age + educ + race + nodegree + married +
#> re74 + re75, data = lalonde, method = "full", estimand = "ATE",
#> caliper = c(0.1, age = 2, educ = 1), std.caliper = c(TRUE,
#> FALSE, FALSE))
#>
#> Summary of Balance for All Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5774 0.1822 1.7569 0.9211 0.3774
#> age 25.8162 28.0303 -0.2419 0.4400 0.0813
#> educ 10.3459 10.2354 0.0448 0.4959 0.0347
#> raceblack 0.8432 0.2028 1.6708 . 0.6404
#> racehispan 0.0595 0.1422 -0.2774 . 0.0827
#> racewhite 0.0973 0.6550 -1.4080 . 0.5577
#> nodegree 0.7081 0.5967 0.2355 . 0.1114
#> married 0.1892 0.5128 -0.7208 . 0.3236
#> re74 2095.5737 5619.2365 -0.5958 0.5181 0.2248
#> re75 1532.0553 2466.4844 -0.2870 0.9563 0.1342
#> eCDF Max
#> distance 0.6444
#> age 0.1577
#> educ 0.1114
#> raceblack 0.6404
#> racehispan 0.0827
#> racewhite 0.5577
#> nodegree 0.1114
#> married 0.3236
#> re74 0.4470
#> re75 0.2876
#>
#> Summary of Balance for Matched Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.3514 0.3474 0.0179 1.0164 0.0145
#> age 22.4088 22.0286 0.0415 0.8461 0.0153
#> educ 10.6993 10.6449 0.0220 1.0801 0.0104
#> raceblack 0.4618 0.4586 0.0083 . 0.0032
#> racehispan 0.1497 0.1083 0.1387 . 0.0414
#> racewhite 0.3885 0.4331 -0.1125 . 0.0446
#> nodegree 0.5792 0.5832 -0.0085 . 0.0040
#> married 0.2894 0.2677 0.0482 . 0.0217
#> re74 2714.6558 2962.5876 -0.0419 1.0862 0.0403
#> re75 1475.1287 1750.0997 -0.0845 1.2293 0.0494
#> eCDF Max Std. Pair Dist.
#> distance 0.0625 0.0448
#> age 0.1049 0.1251
#> educ 0.0549 0.2084
#> raceblack 0.0032 0.0325
#> racehispan 0.0414 0.5148
#> racewhite 0.0446 0.3771
#> nodegree 0.0040 0.2018
#> married 0.0217 0.5360
#> re74 0.1935 0.5407
#> re75 0.1452 0.6811
#>
#> Sample Sizes:
#> Control Treated
#> All 429. 185.
#> Matched (ESS) 135.7 39.63
#> Matched 203. 111.
#> Unmatched 226. 74.
#> Discarded 0. 0.
#>
# Subclassification on a logistic PS with 10 subclasses after
# discarding controls outside common support of PS
s.out1 <- matchit(treat ~ age + educ + race + nodegree +
married + re74 + re75, data = lalonde,
method = "subclass", distance = "glm",
discard = "control", subclass = 10)
s.out1
#> A matchit object
#> - method: Subclassification (10 subclasses)
#> - distance: Propensity score [common support]
#> - estimated with logistic regression
#> - common support: control units dropped
#> - number of obs.: 614 (original), 557 (matched)
#> - target estimand: ATT
#> - covariates: age, educ, race, nodegree, married, re74, re75
summary(s.out1, un = TRUE)
#>
#> Call:
#> matchit(formula = treat ~ age + educ + race + nodegree + married +
#> re74 + re75, data = lalonde, method = "subclass", distance = "glm",
#> discard = "control", subclass = 10)
#>
#> Summary of Balance for All Data:
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5774 0.1822 1.7941 0.9211 0.3774
#> age 25.8162 28.0303 -0.3094 0.4400 0.0813
#> educ 10.3459 10.2354 0.0550 0.4959 0.0347
#> raceblack 0.8432 0.2028 1.7615 . 0.6404
#> racehispan 0.0595 0.1422 -0.3498 . 0.0827
#> racewhite 0.0973 0.6550 -1.8819 . 0.5577
#> nodegree 0.7081 0.5967 0.2450 . 0.1114
#> married 0.1892 0.5128 -0.8263 . 0.3236
#> re74 2095.5737 5619.2365 -0.7211 0.5181 0.2248
#> re75 1532.0553 2466.4844 -0.2903 0.9563 0.1342
#> eCDF Max
#> distance 0.6444
#> age 0.1577
#> educ 0.1114
#> raceblack 0.6404
#> racehispan 0.0827
#> racewhite 0.5577
#> nodegree 0.1114
#> married 0.3236
#> re74 0.4470
#> re75 0.2876
#>
#> Summary of Balance Across Subclasses
#> Means Treated Means Control Std. Mean Diff. Var. Ratio eCDF Mean
#> distance 0.5774 0.5710 0.0293 0.9338 0.0158
#> age 25.8162 25.3714 0.0622 0.4577 0.0866
#> educ 10.3459 10.4094 -0.0316 0.6894 0.0150
#> raceblack 0.8432 0.8262 0.0469 . 0.0170
#> racehispan 0.0595 0.0676 -0.0343 . 0.0081
#> racewhite 0.0973 0.1062 -0.0302 . 0.0089
#> nodegree 0.7081 0.6782 0.0658 . 0.0299
#> married 0.1892 0.1785 0.0274 . 0.0107
#> re74 2095.5737 2232.5096 -0.0280 1.3102 0.0449
#> re75 1532.0553 1643.4179 -0.0346 1.4216 0.0472
#> eCDF Max
#> distance 0.0541
#> age 0.3043
#> educ 0.0425
#> raceblack 0.0170
#> racehispan 0.0081
#> racewhite 0.0089
#> nodegree 0.0299
#> married 0.0107
#> re74 0.2731
#> re75 0.1841
#>
#> Sample Sizes:
#> Control Treated
#> All 429. 185
#> Matched (ESS) 72.59 185
#> Matched 372. 185
#> Unmatched 0. 0
#> Discarded 57. 0
#>
```