stratumStructure: Return structure of matched sets

Description

Tabulate treatment:control ratios occurring in matched sets, and the frequency of their occurrence.

Usage

stratumStructure(stratum,trtgrp=NULL,min.controls=0,max.controls=Inf)

Arguments

stratum

Matched strata, as returned by fullmatch or pairmatch

trtgrp

Dummy variable for treatment group membership. (Not required if stratum is an optmatch object, as returned by fullmatch or pairmatch.)

min.controls

For display, the number of treatment group members per stratum will be truncated at the reciprocal of min.controls.

max.controls

For display, the number of control group members will be truncated at max.controls.

Value

A table showing frequency of occurrence of those treatment:control ratios that occur.
The effective sample size of the stratification, in matched pairs. Given as an attribute of the table, named comparable.num.matched.pairs; see Note.

References

Kalton, G. (1968), Standardization: A technique to control for extraneous variables, Applied Statistics, 17, 118--136.

Hansen, B.B. (2004), Full Matching in an Observational Study of Coaching for the SAT, Journal of the American Statistical Association, 99, 609--618.

Hansen B.B. and Bowers, J. (2008), Covariate balance in simple, stratified and clustered comparative studies, Statistical Science, 23, to appear.

Examples

Run this code

data(plantdist)

plantsfm <- fullmatch(plantdist) # A full match with unrestricted
                                 # treatment-control balance
plantsfm1 <- fullmatch(plantdist,min.controls=2, max.controls=3)

stratumStructure(plantsfm)
stratumStructure(plantsfm1)
stratumStructure(plantsfm, max.controls=4)