balanceUV {Matching}R Documentation

Univariate Balance Tests

Description

This function provides a number of univariate balance metrics. Generally, users should call MatchBalance and not this function directly.

Usage

balanceUV(Tr, Co, weights = rep(1, length(Co)), exact = FALSE, ks=FALSE,
          nboots = 1000, paired=TRUE, match=FALSE,
          weights.Tr=rep(1,length(Tr)), weights.Co=rep(1,length(Co)),
          estimand="ATT")

Arguments

Tr A vector containing the treatment observations.
Co A vector containing the control observations.
weights A vector containing the observation specific weights. Only use this option when the treatment and control observations are paired (as they are after matching).
exact A logical flag indicating if the exact Wilcoxon test should be used instead of the test with a correction. See wilcox.test for details.
ks A logical flag for if the univariate bootstrap Kolmogorov-Smirnov (KS) test should be calculated. If the ks option is set to true, the univariate KS test is calculated for all non-dichotomous variables. The bootstrap KS test is consistent even for non-continuous variables. See ks.boot for more details.
nboots The number of bootstrap samples to be run for the ks test. If zero, no bootstraps are done. Bootstrapping is highly recommended because the bootstrapped Kolmogorov-Smirnov test only provides correct coverage even for non-continuous covariates. At least 500 nboots (preferably 1000) are recommended for publication quality p-values.
paired A flag for if the paired t.test should be used.
match A flag for if the Tr and Co objects are the result of a call to Match.
weights.Tr A vector of weights for the treated observations.
weights.Co A vector of weights for the control observations.
estimand This determines if the standardized mean difference returned by the sdiff object is standardized by the variance of the treatment observations (which is done if the estimand is either "ATE" or "ATT") or by the variance of the control observations (which is done if the estimand is "ATC").

Value

sdiff This is the standardized difference between the treated and control units multiplied by 100. That is, 100 times the mean difference between treatment and control units divided by the standard deviation of the treatment observations alone if the estimand is either ATT or ATE. The variance of the control observations are used if the estimand is ATC.
sdiff.pooled This is the standardized difference between the treated and control units multiplied by 100 using the pooled variance. That is, 100 times the mean difference between treatment and control units divided by the pooled standard deviation as in Rosenbaum and Rubin (1985).
mean.Tr The mean of the treatment group.
mean.Co The mean of the control group.
var.Tr The variance of the treatment group.
var.Co The variance of the control group.
p.value The p-value from the two-sided weighted t.test.
var.ratio var.Tr/var.Co.
ks The object returned by ks.boot.
tt The object returned by two-sided weighted t.test.
qqsummary The return object from a call to qqstats with standardization—i.e., balance test based on the empirical CDF.
qqsummary.raw The return object from a call to qqstats without standardization–i.e., balance tests based on the empirical QQ-plot which retain the scale of the variable.

Author(s)

Jasjeet S. Sekhon, UC Berkeley, sekhon@berkeley.edu, http://sekhon.berkeley.edu/.

References

Sekhon, Jasjeet S. 2011. "Multivariate and Propensity Score Matching Software with Automated Balance Optimization.” Journal of Statistical Software 42(7): 1-52. http://www.jstatsoft.org/v42/i07/

Diamond, Alexis and Jasjeet S. Sekhon. 2005. "Genetic Matching for Estimating Causal Effects: A General Multivariate Matching Method for Achieving Balance in Observational Studies.” Working Paper. http://sekhon.berkeley.edu/papers/GenMatch.pdf

Sekhon, Jasjeet Singh and Richard D. Grieve. 2011. "A Matching Method For Improving Covariate Balance in Cost-Effectiveness Analyses." Health Economics. forthcoming.

Sekhon, Jasjeet S. 2006. ``Alternative Balance Metrics for Bias Reduction in Matching Methods for Causal Inference.'' Working Paper. http://sekhon.berkeley.edu/papers/SekhonBalanceMetrics.pdf

Rosenbaum, Paul R. and Donald B. Rubin. 1985. ``Constructing a Control Group Using Multivariate Matched Sampling Methods That Incorporate the Propensity Score.'' The American Statistician 39:1 33-38.

Hollander, Myles and Douglas A. Wolfe. 1973. Nonparametric statistical inference. New York: John Wiley & Sons.

See Also

Also see summary.balanceUV, qqstats ks.boot, Match, GenMatch, MatchBalance, GerberGreenImai, lalonde

Examples

data(lalonde)
attach(lalonde)

foo  <- balanceUV(re75[treat==1],re75[treat!=1])
summary(foo)


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