optmatch (version 0.8-0)

caliper: Prepare matching distances suitable for matching within calipers.

Description

Encodes calipers, or maximum allowable distances within which to match. The result of a call to caliper is itself a distance specification between treated and control units that can be used with pairmatch() or fullmatch(). Calipers can also be combined with other distance specifications for richer matching problems.

Usage

## S3 method for class 'InfinitySparseMatrix':
caliper(x, width = 1,
    exclude = c(), compare = `<=`)< p="">
  ## S3 method for class 'matrix':
caliper(x, width = 1, exclude = c(),
    compare = `<=`)< p="">
  ## S3 method for class 'optmatch.dlist':
caliper(x, width = 1,
    exclude = c(), compare = `

Arguments

x

A distance specification created with match_on or similar.

width

The width of the caliper: how wide of a margin to allow in matches.

exclude

(Optional) A character vector of observations (corresponding to row and column names) to exclude from the caliper.

compare

A function that decides that whether two observations are with the caliper. The default is `<=`< code="">. `<`< code=""> is a common alternative.

Value

• A matrix like object that is suitable to be given as distance argument to fullmatch or pairmatch. The caliper will be only zeros and Inf values, indicating a possible match or no possible match, respectively.

  You can combine the results of caliper with other distances using the `+` operator. See the examples for usage.

Details

caliper is a generic function with methods for any of the allowed distance specifications: user created matrices, the results of match_on, the results of exactMatch, or combinations (using `+`) of these objects.

width provides the size of the caliper, the allowable distance for matching. If the distance between a treated and control pair is less than or equal to this distance, it is allowed kept; otherwise, the pair is discarded from future matching. The default comparison of ``equal or less than can'' be changed to any other comparison function using the comparison argument.

If you wish to exclude specific units from the caliper requirements, pass the names of these units in the exclude argument. These units will be allowed to match any other unit.

References

P.~R. Rosenbaum and D.~B. Rubin (1985), Constructing a control group using multivariate matched sampling methods that incorporate the propensity score, The American Statistician, 39 33--38.

See Also

exactMatch, match_on, fullmatch, pairmatch

Examples

data(nuclearplants)
# as.matrix() used for convenient presentation only

### Caliper  of .2 pooled SDs in the propensity score
ppty <- glm(pr ~ . - (pr + cost), family = binomial(), data = nuclearplants)
ppty.dist <- match_on(ppty)

as.matrix(pptycaliper <- caliper(ppty.dist, width = .2)) 

### caliper on the Mahalanobis distance
as.matrix(caliper(match_on(pr ~ t1 + t2, data = nuclearplants), width = 3))

### Combining a Mahalanobis distance matching with a caliper
### of 1 pooled SD in the propensity score:
as.matrix(mhd.pptyc <- caliper(ppty.dist, width = 1) +
          match_on(pr ~ t1 + t2, data = nuclearplants))
pairmatch(mhd.pptyc)

### Excluding observations from caliper requirements:
as.matrix(caliper(match_on(pr ~ t1 + t2, data = nuclearplants), width = 3, exclude = c("A", "f")))