`cobalt`

with Other
Preprocessing PackagesThis is an appendix to the main vignette, “Covariate Balance Tables
and Plots: A Guide to the cobalt Package”. It contains descriptions and
demonstrations of several utility functions in `cobalt`

and
the use of `bal.tab()`

with `twang`

,
`Matching`

, `optmatch`

, `CBPS`

,
`ebal`

, `designmatch`

, `sbw`

,
`MatchThem`

, and `cem`

. Note that
`MatchIt`

can perform most of the functions that
`Matching`

, `optmatch`

, and `cem`

can,
and `WeightIt`

can perform most of the functions that
`twang`

, `CBPS`

, `ebal`

, and
`sbw`

can. Because `cobalt`

has been optimized to
work with `MatchIt`

and `WeightIt`

, it is
recommended to use those packages to simplify preprocessing and balance
assessment, but we recognize users may prefer to use the packages
described in this vignette.

In addition to its main balance assessment functions,
`cobalt`

contains several utility functions. These are meant
to reduce the typing and programming burden that often accompany the use
of R with a diverse set of packages.

`splitfactor()`

and `unsplitfactor()`

Some functions (outside of `cobalt`

) are not friendly to
factor or character variables, and require numeric variables to operate
correctly. For example, some regression-style functions, such as
`ebalance()`

in `ebal`

, can only take in
non-singular numeric matrices. Other functions will process factor
variables, but will return output in terms of dummy coded version of the
factors. For example, `lm()`

will create dummy variables out
of a factor and drop the reference category to create regression
coefficients.

To prepare data sets for use in functions that do not allow factors
or to mimic the output of functions that split factor variables, users
can use `splitfactor()`

, which takes in a data set and the
names of variables to split, and outputs a new data set with newly
created dummy variables. Below is an example splitting the
`race`

variable in the Lalonde data set into dummies,
eliminating the reference category (`"black"`

):

treat | age | educ | race | married | nodegree | re74 | re75 | re78 |
---|---|---|---|---|---|---|---|---|

1 | 37 | 11 | black | 1 | 1 | 0 | 0 | 9930.0460 |

1 | 22 | 9 | hispan | 0 | 1 | 0 | 0 | 3595.8940 |

1 | 30 | 12 | black | 0 | 0 | 0 | 0 | 24909.4500 |

1 | 27 | 11 | black | 0 | 1 | 0 | 0 | 7506.1460 |

1 | 33 | 8 | black | 0 | 1 | 0 | 0 | 289.7899 |

1 | 22 | 9 | black | 0 | 1 | 0 | 0 | 4056.4940 |

treat | age | educ | race_hispan | race_white | married | nodegree | re74 | re75 | re78 |
---|---|---|---|---|---|---|---|---|---|

1 | 37 | 11 | 0 | 0 | 1 | 1 | 0 | 0 | 9930.0460 |

1 | 22 | 9 | 1 | 0 | 0 | 1 | 0 | 0 | 3595.8940 |

1 | 30 | 12 | 0 | 0 | 0 | 0 | 0 | 0 | 24909.4500 |

1 | 27 | 11 | 0 | 0 | 0 | 1 | 0 | 0 | 7506.1460 |

1 | 33 | 8 | 0 | 0 | 0 | 1 | 0 | 0 | 289.7899 |

1 | 22 | 9 | 0 | 0 | 0 | 1 | 0 | 0 | 4056.4940 |

It is possible to undo the action of `splitfactor()`

with
`unsplitfactor()`

, which takes in a data set with dummy
variables formed from `splitfactor()`

or otherwise and
recreates the original factor variable. If the reference category was
dropped, its value needs to be supplied.

```
lalonde.unsplit <- unsplitfactor(lalonde.split, "race",
dropped.level = "black")
head(lalonde.unsplit)
```

treat | age | educ | race | married | nodegree | re74 | re75 | re78 |
---|---|---|---|---|---|---|---|---|

1 | 37 | 11 | black | 1 | 1 | 0 | 0 | 9930.0460 |

1 | 22 | 9 | hispan | 0 | 1 | 0 | 0 | 3595.8940 |

1 | 30 | 12 | black | 0 | 0 | 0 | 0 | 24909.4500 |

1 | 27 | 11 | black | 0 | 1 | 0 | 0 | 7506.1460 |

1 | 33 | 8 | black | 0 | 1 | 0 | 0 | 289.7899 |

1 | 22 | 9 | black | 0 | 1 | 0 | 0 | 4056.4940 |

Notice the original data set and the unsplit data set look identical.
If the input to `unsplitfactor()`

is the output of a call to
`splitfactor()`

(as it was here), you don’t need to tell
`unsplitfactor()`

the name of the split variable or the value
of the dropped level. It was done here for illustration purposes.

`get.w()`

`get.w()`

allows users to extract weights from the output
of a call to a preprocessing function in one of the supported packages.
Because each package stores weights in different ways, it can be helpful
to have a single function that applies equally to all outputs.
`twang`

has a function called `get.weights()`

that
performs the same functions with slightly finer control for the output
of a call to `ps()`

.

`bal.tab()`

The next sections describe the use of `bal.tab()`

with
packages other than those described in the main vignette. Even if you
are using `bal.tab()`

with one of these packages, it may be
useful to read the main vignette to understand `bal.tab()`

’s
main options, which are not detailed here.

`bal.tab()`

with `twang`

Generalized boosted modeling (GBM), as implemented in
`twang`

, can be an effective way to generate propensity
scores and weights for use in propensity score weighting.
`bal.tab()`

functions similarly to the functions
`bal.table()`

and `summary()`

when used with GBM
in `twang`

. Below is a simple example of its use:

```
#GBM PS weighting for the ATT
data("lalonde", package = "cobalt") ##If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78))
f <- reformulate(names(covs0), "treat")
ps.out <- twang::ps(f, data = lalonde,
stop.method = c("es.mean", "es.max"),
estimand = "ATT", n.trees = 1000,
verbose = FALSE)
bal.tab(ps.out, stop.method = "es.mean")
```

```
## Balance Measures
## Type Diff.Adj
## prop.score Distance 0.5189
## age Contin. 0.0400
## educ Contin. -0.0819
## race_black Binary 0.0687
## race_hispan Binary -0.0032
## race_white Binary -0.0817
## married Binary -0.0296
## nodegree Binary 0.1901
## re74 Contin. 0.0691
## re75 Contin. 0.0953
##
## Effective sample sizes
## Control Treated
## Unadjusted 429. 185
## Adjusted 33.03 185
```

The output looks a bit different from `twang`

’s
`bal.table()`

output. First is the original call to
`ps()`

. Next is the balance table containing mean differences
for the covariates included in the input to `ps()`

. Last is a
table displaying sample size information, similar to what would be
generated using `twang`

’s `summary()`

function.
The “effective” sample size is displayed when weighting is used; it is
calculated as is done in `twang`

. See the `twang`

documentation, `?bal.tab`

, or “Details on Calculations” in
the main vignette for details on this calculation.

When using `bal.tab()`

with `twang`

, the user
must specify the `ps`

object, the output of a call to
`ps()`

, as the first argument. The second argument,
`stop.method`

, is the name of the stop method(s) for which
balance is to be assessed, since a `ps`

object may contain
more than one if so specified. `bal.tab()`

can display the
balance for more than one stop method at a time by specifying a vector
of stop method names. If this argument is left empty or if the argument
to `stop.method`

does not correspond to any of the stop
methods in the `ps`

object, `bal.tab()`

will
default to displaying balance for all stop methods available.
Abbreviations are allowed for the stop method, which is not case
sensitive.

The other arguments to `bal.tab()`

when using it with
`twang`

have the same form and function as those given when
using it without a conditioning package, except for
`s.d.denom`

. If the estimand of the stop method used is the
ATT, `s.d.denom`

will default to `"treated"`

if
not specified, and if the estimand is the ATE, `s.d.denom`

will default to `"pooled"`

, mimicking the behavior of
`twang`

. The user can specify their own argument to
`s.d.denom`

, but using the defaults is advised.

If sampling weights are used in the call to `ps()`

, they
will be automatically incorporated into the `bal.tab()`

calculations for both the adjusted and unadjusted samples, just as
`twang`

does.

`mnps`

objects resulting from fitting models in
`twang`

with multi-category treatments are also compatible
with `cobalt`

. See the section “Using `cobalt`

with multi-category treatments” in the main vignette. `iptw`

objects resulting from fitting models in `twang`

with
longitudinal treatments are also compatible with `cobalt`

.
See the Appendix 3 vignette. `ps.cont`

objects resulting from
using `ps.cont()`

in `twangContinuous`

, which
implements GBM for continuous treatments, are also compatible. See the
section “Using `cobalt`

with continuous treatments” in the
main vignette.

`bal.tab()`

with `Matching`

The `Matching`

package is used for propensity score
matching, and was also the first package to implement genetic matching.
`MatchIt`

calls `Matching`

to use genetic matching
and can accomplish many of the matching methods `Matching`

can, but `Matching`

is still a widely used package with its
own strengths. `bal.tab()`

functions similarly to
`Matching`

’s `MatchBalance()`

command, which
yields a thorough presentation of balance. Below is a simple example of
the use of `bal.tab()`

with `Matching`

:

```
#1:1 NN PS matching w/ replacement
data("lalonde", package = "cobalt") #If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78))
f <- reformulate(names(covs0), "treat")
fit <- glm(f, data = lalonde, family = binomial)
p.score <- fit$fitted.values
match.out <- Matching::Match(Tr = lalonde$treat, X = p.score,
estimand = "ATT")
bal.tab(match.out, formula = f, data = lalonde,
distance = ~ p.score)
```

```
## Balance Measures
## Type Diff.Adj
## p.score Distance 0.0043
## age Contin. 0.2106
## educ Contin. 0.0201
## race_black Binary 0.0149
## race_hispan Binary -0.0217
## race_white Binary -0.0009
## married Binary 0.1688
## nodegree Binary -0.0173
## re74 Contin. -0.0772
## re75 Contin. -0.0127
##
## Sample sizes
## Control Treated
## All 429. 185
## Matched (ESS) 49.17 185
## Matched (Unweighted) 136. 185
## Unmatched 293. 0
```

The output looks quite different from `Matching`

’s
`MatchBalance()`

output. Rather than being stacked
vertically, balance statistics are arranged horizontally in a table
format, allowing for quick balance checking. Below the balance table is
a summary of the sample size before and after matching, similar to what
`Matching`

’s `summary()`

command would display.
The sample size can include an “ESS” and “unweighted” value; the “ESS”
value is the effective sample size resulting from the matching weights,
while the “unweighted” is the count of units with nonzero matching
weights.

The input to `bal.tab()`

is similar to that given to
`MatchBalance()`

: the `Match`

object resulting
from the call to `Match()`

, a formula relating treatment to
the covariates for which balance is to be assessed, and the original
data set. This is not the only way to call `bal.tab()`

:
instead of a formula and a data set, one can also input a data frame of
covariates and a vector of treatment status indicators, just as when
using `bal.tab()`

without a conditioning package. For
example, the code below will yield the same results as the call to
`bal.tab()`

above:

The other arguments to `bal.tab()`

when using it with
`Matching`

have the same form and function as those given
when using it without a conditioning package, except for
`s.d.denom`

. If the estimand of the original call to
`Match()`

is the ATT, `s.d.denom`

will default to
`"treated"`

if not specified; if the estimand is the ATE,
`s.d.denom`

will default to `"pooled"`

; if the
estimand is the ATC, `s.d.denom`

will default to
`"control"`

. The user can specify their own argument to
`s.d.denom`

, but using the defaults is advisable. In
addition, the use of the `addl`

argument is unnecessary
because the covariates are entered manually as arguments, so all
covariates for which balance is to be assessed can be entered through
the `formula`

or `covs`

argument. If the
covariates are stored in two separate data frames, it may be useful to
include one in `formula`

or `covs`

and the other
in `addl`

.

`bal.tab()`

with `optmatch`

The `optmatch`

package is useful for performing optimal
pairwise or full matching. Most functions in `optmatch`

are
subsumed in `MatchIt`

, but `optmatch`

sees use
from those who want finer control of the matching process than
`MatchIt`

allows. The output of calls to functions in
`optmatch`

is an `optmatch`

object, which contains
matching stratum membership for each unit in the given data set. Units
that are matched with each other are assigned the same matching stratum.
The user guide for `optmatch`

recommends using the
`RItools`

package for balance assessment, but below is an
example of how to use `bal.tab()`

for the same purpose. Note
that some results will differ between `cobalt`

and
`RItools`

because of differences in how balance is calculated
in each.

```
#Optimal full matching on the propensity score
data("lalonde", package = "cobalt") #If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78))
f <- reformulate(names(covs0), "treat")
fit <- glm(f, data = lalonde, family = binomial)
p.score <- fit$fitted.values #get the propensity score
fm <- optmatch::fullmatch(treat ~ p.score, data = lalonde)
bal.tab(fm, covs = covs0, distance = ~ p.score)
```

```
## Balance Measures
## Type Diff.Adj
## p.score Distance 0.0058
## age Contin. 0.1641
## educ Contin. -0.0215
## race_black Binary 0.0236
## race_hispan Binary -0.0066
## race_white Binary -0.0237
## married Binary 0.1471
## nodegree Binary -0.0001
## re74 Contin. -0.0639
## re75 Contin. -0.0112
##
## Sample sizes
## Control Treated
## All 429. 185
## Matched (ESS) 51.3 185
## Matched (Unweighted) 429. 185
```

Most details for the use of `bal.tab()`

with
`optmatch`

are similar to those when using
`bal.tab()`

with `Matching`

. Users can enter
either a formula and a data set or a vector of treatment status and a
set of covariates. Unlike with `Matching`

, entering the
treatment variable is optional as it is already stored in the
`optmatch`

object. `bal.tab()`

is compatible with
both `pairmatch()`

and `fullmatch()`

output.

`bal.tab()`

with `CBPS`

The `CBPS`

(Covariate Balancing Propensity Score) package
is a great tool for generating covariate balancing propensity scores, a
class of propensity scores that are quite effective at balancing
covariates among groups. `CBPS`

includes functions for
estimating propensity scores for binary, multi-category, and continuous
treatments. `bal.tab()`

functions similarly to
`CBPS`

’s `balance()`

command. Below is a simple
example of its use with a binary treatment:

```
#CBPS weighting
data("lalonde", package = "cobalt") #If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78))
f <- reformulate(names(covs0), "treat")
#Generating covariate balancing propensity score weights for ATT
cbps.out <- CBPS::CBPS(f, data = lalonde)
```

`## [1] "Finding ATT with T=1 as the treatment. Set ATT=2 to find ATT with T=0 as the treatment"`

```
## Balance Measures
## Type Diff.Adj
## prop.score Distance -0.0057
## age Contin. -0.0052
## educ Contin. -0.0017
## race_black Binary 0.0053
## race_hispan Binary -0.0009
## race_white Binary -0.0057
## married Binary -0.0073
## nodegree Binary 0.0092
## re74 Contin. -0.0078
## re75 Contin. 0.0061
##
## Effective sample sizes
## Control Treated
## Unadjusted 429. 185
## Adjusted 99.97 185
```

First is the original call to `CBPS()`

. Next is the
balance table containing mean differences for the covariates included in
the input to `CBPS()`

. Last is a table displaying sample size
information. The “effective” sample size is displayed when weighting
(rather than matching or subclassification) is used; it is calculated as
is done in `twang`

. See the `twang`

documentation,
`?bal.tab`

, or “Details on Calculations” in the main vignette
for details on this calculation.

The other arguments to `bal.tab()`

when using it with
`CBPS`

have the same form and function as those given when
using it without a conditioning package, except for
`s.d.denom`

. If the estimand of the original call to
`CBPS()`

is the ATT, `s.d.denom`

will default to
`"treated"`

if not specified, and if the estimand is the ATE,
`s.d.denom`

will default to `"pooled"`

. The user
can specify their own argument to `s.d.denom`

, but using the
defaults is advisable.

`CBPSContinuous`

objects resulting from fitting models in
`CBPS`

with continuous treatments are also compatible with
`cobalt`

. See the section “Using `cobalt`

with
continuous treatments” in the main vignette. `CBPS`

objects
resulting from fitting models in `CBPS`

with multi-category
treatments are also compatible with `cobalt`

. See the section
“Using `cobalt`

with multi-category treatments” in the main
vignette. `CBMSM`

objects resulting from fitting models in
`CBPS`

with longitudinal treatments are also compatible with
`cobalt`

. See the Appendix 3 vignette.

`bal.tab()`

with `ebal`

The `ebal`

package implements entropy balancing, a method
of weighting for the ATT that yields perfect balance on all desired
moments of the covariate distributions between groups. Rather than
estimate a propensity score, entropy balancing generates weights
directly that satisfy a user-defined moment condition, specifying which
moments are to be balanced. Note that all the functionality of
`ebal`

is contained within `Weightit`

.
`ebal`

does not have its own balance assessment function;
thus, `cobalt`

is the only way to assess balance without
programming, which the `ebal`

documentation instructs. Below
is a simple example of using `bal.tab()`

with
`ebal`

:

```
#Entropy balancing
data("lalonde", package = "cobalt") #If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78, race))
#Generating entropy balancing weights
e.out <- ebal::ebalance(lalonde$treat, covs0)
```

`## Converged within tolerance`

```
## Balance Measures
## Type Diff.Adj
## age Contin. -0
## educ Contin. -0
## married Binary -0
## nodegree Binary 0
## re74 Contin. -0
## re75 Contin. -0
##
## Effective sample sizes
## Control Treated
## Unadjusted 429. 185
## Adjusted 247.64 185
```

First is the balance table containing mean differences for covariates
included in the original call to `ebalance`

. In general,
these will all be very close to 0. Next is a table displaying effective
sample size information. See `?bal.tab`

or “Details on
Calculations” in the main vignette for details on this calculation. A
common issue when using entropy balancing is small effective sample
size, which can yield low precision in effect estimation when using
weighted regression, so it is important that users pay attention to this
measure.

The input is similar to that for using `bal.tab()`

with
`Matching`

or `optmatch`

. In addition to the
`ebalance`

object, one must specify either both a formula and
a data set or both a treatment vector and a data frame of
covariates.

`bal.tab()`

with `designmatch`

The `designmatch`

package implements various matching
methods that use optimization to find matches that satisfy certain
balance constraints. `bal.tab()`

functions similarly to
`designmatch`

’s `meantab()`

command but provides
additional flexibility and convenience. Below is a simple example of
using `bal.tab()`

with `designmatch`

:

```
#Mixed integer programming matching
library("designmatch")
data("lalonde", package = "cobalt") #If not yet loaded
covs0 <- subset(lalonde, select = -c(treat, re78, race))
#Matching for balance on covariates
dmout <- bmatch(lalonde$treat,
dist_mat = NULL,
subset_weight = NULL,
mom = list(covs = covs0,
tols = absstddif(covs0, lalonde$treat, .005)),
n_controls = 1,
total_groups = 185)
```

```
## Building the matching problem...
## HiGHS optimizer is open...
## Finding the optimal matches...
## Optimal matches found
## HiGHS optimizer is open...
## Finding the optimal matches...
## Optimal matches found
```

```
## Balance Measures
## Type Diff.Adj
## age Contin. -0.0106
## educ Contin. 0.0081
## married Binary -0.0138
## nodegree Binary 0.0119
## re74 Contin. -0.0105
## re75 Contin. 0.0041
##
## Sample sizes
## Control Treated
## All 429 185
## Matched 185 185
## Unmatched 244 0
```

The input is similar to that for using `bal.tab()`

with
`Matching`

or `optmatch`

. In addition to the
`designmatch()`

output object, one must specify either both a
formula and a data set or both a treatment vector and a data frame of
covariates. The output is similar to that of `optmatch`

.

`bal.tab()`

with `sbw`

The `sbw`

package implements optimization-based weighting
to estimate weights that satisfy certain balance constraints and have
minimal variance. `bal.tab()`

functions similarly to
`sbw`

’s `summarize()`

function but provides
additional flexibility and convenience. Below is a simple example of
using `bal.tab()`

with `sbw`

:

```
#Optimization-based weighting
data("lalonde", package = "cobalt") #If not yet loaded
lalonde_split <- splitfactor(lalonde, drop.first = "if2")
cov.names <- setdiff(names(lalonde_split), c("treat", "re78"))
#Estimating balancing weights for the ATT
sbw.out <- sbw::sbw(lalonde_split,
ind = "treat",
bal = list(bal_cov = cov.names,
bal_alg = FALSE,
bal_tol = .001),
par = list(par_est = "att"))
```

```
## quadprog optimizer is opening...
## Finding the optimal weights...
## Optimal weights found.
```

```
## Balance Measures
## Type M.0.Un M.1.Un Diff.Un M.0.Adj M.1.Adj Diff.Adj
## age Contin. 28.0303 25.8162 -0.3094 25.8054 25.8162 0.0015
## educ Contin. 10.2354 10.3459 0.0550 10.3431 10.3459 0.0014
## race_black Binary 0.2028 0.8432 1.7615 0.8428 0.8432 0.0011
## race_hispan Binary 0.1422 0.0595 -0.3498 0.0594 0.0595 0.0003
## race_white Binary 0.6550 0.0973 -1.8819 0.0978 0.0973 -0.0016
## married Binary 0.5128 0.1892 -0.8263 0.1897 0.1892 -0.0013
## nodegree Binary 0.5967 0.7081 0.2450 0.7076 0.7081 0.0011
## re74 Contin. 5619.2365 2095.5737 -0.7211 2102.3624 2095.5737 -0.0014
## re75 Contin. 2466.4844 1532.0553 -0.2903 1528.7633 1532.0553 0.0010
##
## Effective sample sizes
## Control Treated
## Unadjusted 429. 185
## Adjusted 108.99 185
```

The output is similar to the output of a call to
`summarize()`

. Rather than stack several balance tables
vertically, each with their own balance summary, here they are displayed
horizontally. Note that due to differences in how `sbw`

and
`cobalt`

compute the standardization factor in the
standardized mean difference, values may not be identical between
`bal.tab()`

and `summarize()`

. Also note that
`bal.tab()`

’s default is to display raw rather than
standardized mean differences for binary variables.

`bal.tab()`

with `MatchThem`

The `MatchThem`

package is essentially a wrapper for
`matchit()`

from `MatchIt`

and
`weightit()`

from `WeightIt`

but for use with
multiply imputed data. Using `bal.tab()`

on
`mimids`

or `wimids`

objects from
`MatchThem`

activates the features that accompany multiply
imputed data; balance is assessed within each imputed dataset and
aggregated across imputations. See `?bal.tab.imp`

or
`vignette("segmented-data")`

for more information about using
`cobalt`

with multiply imputed data. Below is a simple
example of using `bal.tab()`

with `MatchThem`

:

```
#PS weighting on multiply imputed data
data("lalonde_mis", package = "cobalt")
#Generate imputed data sets
m <- 10 #number of imputed data sets
imp.out <- mice::mice(lalonde_mis, m = m, print = FALSE)
#Matching for balance on covariates
mt.out <- MatchThem::matchthem(treat ~ age + educ + married +
race + re74 + re75,
datasets = imp.out,
approach = "within",
method = "nearest",
estimand = "ATT")
bal.tab(mt.out)
```

```
## Balance summary across all imputations
## Type Min.Diff.Adj Mean.Diff.Adj Max.Diff.Adj
## distance Distance 0.9445 0.9539 0.9636
## age Contin. -0.0423 0.0048 0.0544
## educ Contin. -0.1774 -0.1497 -0.1183
## married Binary -0.0414 -0.0204 0.0135
## race_black Binary 1.0259 1.0259 1.0259
## race_hispan Binary -0.8000 -0.7429 -0.7086
## race_white Binary -0.6931 -0.6657 -0.6201
## re74 Contin. -0.1028 -0.0547 -0.0173
## re75 Contin. -0.1016 -0.0598 -0.0324
##
## Average sample sizes across imputations
## 0 1
## All 429 185
## Matched 185 185
## Unmatched 244 0
```

```
#Weighting for balance on covariates
wt.out <- MatchThem::weightthem(treat ~ age + educ + married +
race + re74 + re75,
datasets = imp.out,
approach = "within",
method = "ps",
estimand = "ATE")
bal.tab(wt.out)
```

```
## Balance summary across all imputations
## Type Min.Diff.Adj Mean.Diff.Adj Max.Diff.Adj
## prop.score Distance 0.1411 0.1547 0.1678
## age Contin. -0.1916 -0.1885 -0.1815
## educ Contin. 0.0743 0.0831 0.0919
## married Binary -0.2519 -0.2191 -0.1873
## race_black Binary 0.1321 0.1457 0.1593
## race_hispan Binary 0.0278 0.0361 0.0472
## race_white Binary -0.1871 -0.1682 -0.1492
## re74 Contin. -0.3027 -0.2882 -0.2765
## re75 Contin. -0.1635 -0.1541 -0.1445
##
## Average effective sample sizes across imputations
## 0 1
## Unadjusted 429. 185.
## Adjusted 331.84 66.65
```

The input is similar to that for using `bal.tab()`

with
`MatchIt`

or `WeightIt`

.

`bal.tab()`

with `cem`

The `cem`

package implements coarsened exact matching for
binary and multi-category treatments. `bal.tab()`

functions
similarly to `cems`

’s `imbalance()`

. Below is a
simple example of using `bal.tab()`

with
`cem`

:

```
#Coarsened exact matching
data("lalonde", package = "cobalt") #If not yet loaded
#Matching for balance on covariates
cem.out <- cem::cem("treat", data = lalonde, drop = "re78")
```

```
##
## Using 'treat'='1' as baseline group
```

```
## Balance Measures
## Type Diff.Adj KS.Adj
## age Contin. 0.0512 0.1581
## educ Contin. -0.0441 0.0445
## race_black Binary 0.0000 0.0000
## race_hispan Binary 0.0000 0.0000
## race_white Binary 0.0000 0.0000
## married Binary 0.0000 0.0000
## nodegree Binary 0.0000 0.0000
## re74 Contin. -0.0341 0.2418
## re75 Contin. -0.0528 0.1162
##
## Sample sizes
## Control Treated
## All 429. 185
## Matched (ESS) 36.29 68
## Matched (Unweighted) 78. 68
## Unmatched 351. 117
```

The input is similar to that for using `bal.tab()`

with
`Matching`

or `optmatch`

. In addition to the
`cem()`

output object, one must specify either both a formula
and a data set or both a treatment vector and a data frame of
covariates. Unlike with `Matching`

, entering the treatment
variable is optional as it is already stored in the output object. The
output is similar to that of `optmatch`

.

When using `cem()`

with multiply imputed data (i.e., by
supplying a list of data.frames to the `datalist`

argument in
`cem()`

), an argument to `imp`

should be specified
to `bal.tab()`

or a `mids`

object from the
`mice`

package should be given as the argument to
`data`

. See `?bal.tab.imp`

or
`vignette("segmented-data")`

for more information about using
`cobalt`

with multiply imputed data. Below is an example of
using `cem`

with multiply imputed data from
`mice`

:

```
#Coarsened exact matching on multiply imputed data
data("lalonde_mis", package = "cobalt")
#Generate imputed data sets
m <- 10 #number of imputed data sets
imp.out <- mice::mice(lalonde_mis, m = m, print = FALSE)
imp.data.list <- mice::complete(imp.out, "all")
#Match within each imputed dataset
cem.out.imp <- cem::cem("treat", datalist = imp.data.list,
drop = "re78")
```

```
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
##
## Using 'treat'='1' as baseline group
```

```
## Balance summary across all imputations
## Type Min.Diff.Adj Mean.Diff.Adj Max.Diff.Adj
## age Contin. 0.0461 0.0480 0.0512
## educ Contin. -0.0441 -0.0359 -0.0090
## race_black Binary -0.0000 -0.0000 0.0000
## race_hispan Binary -0.0000 -0.0000 0.0000
## race_white Binary -0.0000 -0.0000 0.0000
## married Binary -0.0000 0.0000 0.0000
## nodegree Binary -0.0000 0.0000 0.0000
## re74 Contin. -0.0394 -0.0344 -0.0326
## re75 Contin. -0.0742 -0.0546 -0.0429
##
## Average sample sizes across imputations
## 0 1
## All 429. 185.
## Matched (ESS) 35.42 66.3
## Matched (Unweighted) 77.8 66.3
## Unmatched 351.2 118.7
```

`bal.tab()`

with other packagesIt is possible to use `bal.tab()`

with objects that don’t
come from these packages using the `default`

method. If an
object that doesn’t correspond to the output from one of the
specifically supported packages is passed as the first argument to
`bal.tab()`

, `bal.tab()`

will do its best to
process that object as if it did come from a supported package. It will
search through the components of the object for items with names like
`"treat"`

, `"covs"`

, `"data"`

,
`"weights"`

, etc., that have the correct object types. Any
additional arguments can be specified by the user.

The goal of the `default`

method is to allow package
authors to rely on `cobalt`

as a substitute for any balancing
function they might otherwise write. By ensuring compatibility with the
`default`

method, package authors can have their users simply
supply the output of a compatible function into `cobalt`

functions without having to write a specific method in
`cobalt`

. A package author would need to make sure the output
of their package contained enough information with correctly named
components; if so, `cobalt`

functions can be used as
conveniently with the output as it is with specifically supported
packages.

Below, we demonstrate this capability with the output of
`optweight`

, which performs a version of propensity score
weighting using optimization, similar to `sbw`

. No
`bal.tab`

method has been written with `optweight`

output in mind; rather, `optweight`

was written to have
output compatible with the `default`

method of
`bal.tab`

.

```
#Optimization-based weighting
data("lalonde", package = "cobalt")
#Estimate the weights using optimization
ow.out <- optweight::optweight(treat ~ age + educ + married + race + re74 + re75,
data = lalonde, estimand = "ATE", tols = .01)
#Note the contents of the output object:
names(ow.out)
```

```
## [1] "weights" "treat" "covs" "s.weights" "estimand" "focal"
## [7] "call" "tols" "duals" "info"
```

```
## Balance Measures
## Type Diff.Adj
## age Contin. -0.0000
## educ Contin. 0.0100
## married Binary -0.0223
## race_black Binary 0.0261
## race_hispan Binary -0.0000
## race_white Binary -0.0252
## re74 Contin. -0.0100
## re75 Contin. 0.0085
##
## Effective sample sizes
## Control Treated
## Unadjusted 429. 185.
## Adjusted 349.42 52.04
```

The output is treated as output from a specifically supported
package. See `?bal.tab.default`

for more details and another
example.