ivmodel (version 1.9.1)

permTest.absBias: Perform a permutation test using the sum of absolute biases

Description

permTest.absBias performs a permutation test for complete randomization using the sum of absolute biases as a test statistic.

Usage

permTest.absBias(X, D = NULL, Z = NULL,
assignment = "complete",
perms = 1000, subclass = NULL)

Value

p-value testing whether or not an indicator (treatment or instrument) is as-if randomized under complete randomization (i.e., random permutations), block randomization (i.e., random permutations within subclasses), or Bernoulli trials.

Arguments

X

Covariate matrix (with units as rows and covariates as columns).

D

Indicator vector for a binary treatment (must contain 1 or 0 for each unit).

Z

Indicator vector for a binary instrument (must contain 1 or 0 for each unit).

assignment

Must be "complete", "block", or "bernoulli". Designates whether to test for complete randomization, block randomization, or Bernoulli trials.

subclass

Vector of subclasses (one for each unit). Subclasses can be numbers or characters, as long as there is one specified for each unit. Only needed if assignment = "block".

perms

Number of permutations used to approximate the permutation test.

Author

Zach Branson and Luke Keele

References

Branson, Z. and Keele, L. (2020). Evaluating a Key Instrumental Variable Assumption Using Randomization Tests. American Journal of Epidemiology. To appear.

Examples

	#load the data
	data(icu.data)
	#the covariate matrix is
	X = as.matrix(subset(icu.data, select = -c(open_bin, icu_bed)))
	#the treatment
	D = icu.data$icu_bed
	#the instrument
	Z = icu.data$open_bin
	#the subclass
	subclass = icu.data$site
	
	#can uncomment the following code for examples
	
	#permutation test for complete randomization (for the treatment)
	#permTest.absBias(X = X, D = D,
	#assignment = "complete", perms = 500)
	#permutation test for complete randomization (for the instrument)
	#permTest.absBias(X = X, D = D, Z = Z,
	#assignment = "complete", perms = 500)
	#permutation test for block randomization (for the treatment)
	#permTest.absBias(X = X, D = D,
	#assignment = "block", subclass = subclass, perms = 500)
	#permutation test for block randomization (for the instrument)
	#permTest.absBias(X = X, D = D, Z = Z,
	#assignment = "block",
	#subclass = subclass, perms = 500)
	#permutation test for bernoulli trials (for the treatment)
	#permTest.absBias(X = X, D = D,
	#assignment = "bernoulli", perms = 500)
	#permutation test for bernoulli randomization (for the instrument)
	#permTest.absBias(X = X, D = D, Z = Z,
	#assignment = "bernoulli", perms = 500)