MatchIt: add_s.weights – R documentation

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add_s.weights

Add sampling weights to a matchit object

Description

Adds sampling weights to a matchit object so that they are incorporated into balance assessment and creation of the weights. This would typically only be used when an argument to s.weights was not supplied to matchit (i.e., because they were not to be included in the estimation of the propensity score) but sampling weights are required for generalizing an effect to the correct population. Without adding sampling weights to the matchit object, balance assessment tools (i.e., summary.matchit and plot.matchit) will not calculate balance statistics correctly, and the weights produced by match.data and get_matches will not incorporate the sampling weights.

Usage

add_s.weights(m, s.weights = NULL, data = NULL)

Arguments

`m`	a `matchit` object; the output of a call to `matchit`, typically with the `s.weights` argument unspecified.
`s.weights`	an numeric vector of sampling weights to be added to the `matchit` object. 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`).
`data`	a data frame containing the sampling weights if given as a string or formula. If unspecified, `add_s.weights` will attempt to find the dataset using the environment of the `matchit` object.

Value

a matchit object with an s.weights component containing the supplied sampling weights. The nn component containing the sample sizes before and after matching will be adjusted to incorporate the sampling weights. If s.weights = NULL, the original matchit object is returned.

Author(s)

Noah Greifer

Examples

data("lalonde")

# Generate random sampling weights, just
# for this example
sw <- rchisq(nrow(lalonde), 2)

# NN PS match using logistic regression PS that doesn't
# include sampling weights
m.out <- matchit(treat ~ age + educ + race + nodegree +
                   married  + re74 + re75, data = lalonde)

m.out

# Add s.weights to the matchit object
m.out <- add_s.weights(m.out, sw)

m.out #note additional output

# Check balance; note that sample sizes incorporate
# s.weights
summary(m.out, improvement = FALSE)

MatchIt

Nonparametric Preprocessing for Parametric Causal Inference

v4.1.0

GPL (>= 2)

Authors

Daniel Ho [aut] (<https://orcid.org/0000-0002-2195-5469>), Kosuke Imai [aut] (<https://orcid.org/0000-0002-2748-1022>), Gary King [aut] (<https://orcid.org/0000-0002-5327-7631>), Elizabeth Stuart [aut] (<https://orcid.org/0000-0002-9042-8611>), Alex Whitworth [ctb], Noah Greifer [ctb, cre, aut] (<https://orcid.org/0000-0003-3067-7154>)

Initial release