Optmatch Class

The optmatch class describes the results of an optimal full matching (using either fullmatch or pairmatch). For the most part, these objects can be treated as factors.

The summary function quantifies optmatch objects on the effective sample size, the distribution of distances between matched units, and how well the match reduces average differences.

Usage

# S3 method for optmatch
summary(
  object,
  propensity.model = NULL,
  ...,
  min.controls = 0.2,
  max.controls = 5,
  quantiles = c(0, 0.5, 0.95, 1)
)

Arguments

object

The optmatch object to summarize.

propensity.model

An optional propensity model (the result of a call to glm) to use when summarizing the match. If the RItools package is installed, an additional chi-squared test will be performed on the average differences between treated and control units on each variable used in the model. See the xBalance function in the RItools package for more details.

...

Additional arguments to pass to xBalance when also passing a propensity model.

min.controls

To minimize the the display of a groups with many treated and few controls, all groups with more than 5 treated units will be summarized as “5+”. This is the reciprocal of the default value (1/5 = 0.2). Lower this value to see more groups.

max.controls

Like min.controls sets maximum group sized displayed with respect to the number of controls. Raise this value to see more groups.

quantiles

A points in the ECDF at which the distances between units will be displayed.

Value

optmatch.summary

Details

optmatch objects descend from factor. Elements of this vector correspond to members of the treatment and control groups in reference to which the matching problem was posed, and are named accordingly; the names are taken from the row and column names of distance. Each element of the vector is either NA, indicating unavailability of any suitable matches for that element, or the concatenation of: (i) a character abbreviation of the name of the subclass (as encoded using exactMatch) (ii) the string .; and (iii) a non-negative integer. In this last place, positive whole numbers indicate placement of the unit into a matched set and NA indicates that all or part of the matching problem given to fullmatch was found to be infeasible. The functions matched, unmatched, and matchfailed distinguish these scenarios.

Secondarily, fullmatch returns various data about the matching process and its result, stored as attributes of the named vector which is its primary output. In particular, the exceedances attribute gives upper bounds, not necessarily sharp, for the amount by which the sum of distances between matched units in the result of fullmatch exceeds the least possible sum of distances between matched units in a feasible solution to the matching problem given to fullmatch. (Such a bound is also printed by print.optmatch and summary.optmatch.)

See also

print.optmatch