vcovCR.iv_robust: Cluster-robust variance-covariance matrix for an...

In clubSandwich: Cluster-Robust (Sandwich) Variance Estimators with Small-Sample Corrections

Cluster-robust variance-covariance matrix for an estimatr::iv_robust object.

Description

vcovCR returns a sandwich estimate of the variance-covariance matrix of a set of regression coefficient estimates from an iv_robust object.

Usage

## S3 method for class 'iv_robust'
vcovCR(
  obj,
  cluster,
  type,
  target = NULL,
  inverse_var = FALSE,
  form = "sandwich",
  ...
)

Arguments

obj	Fitted model for which to calculate the variance-covariance matrix
cluster	Vector indicating which observations belong to the same cluster. Required for iv_robust objects unless the model was fitted with a clusters argument.
type	Character string specifying which small-sample adjustment should be used, with available options "CR0", "CR1", "CR1p", "CR1S", "CR2", or "CR3". See "Details" section of vcovCR for further information.
target	Optional matrix or vector describing the working variance-covariance model used to calculate the CR2 and CR4 adjustment matrices. If a vector, the target matrix is assumed to be diagonal. If not specified, the target is taken to be an identity matrix.
inverse_var	Not used for iv_robust objects.
form	Controls the form of the returned matrix. The default "sandwich" will return the sandwich variance-covariance matrix. Alternately, setting form = "meat" will return only the meat of the sandwich and setting form = B, where B is a matrix of appropriate dimension, will return the sandwich variance-covariance matrix calculated using B as the bread. form = "estfun" will return the (appropriately scaled) estimating function, the transposed crossproduct of which is equal to the sandwich variance-covariance matrix.
...	Additional arguments available for some classes of objects.

Value

An object of class c("vcovCR","clubSandwich"), which consists of a matrix of the estimated variance of and covariances between the regression coefficient estimates.

See Also

vcovCR

Examples

if (requireNamespace("estimatr", quietly = TRUE)) withAutoprint({
  library(estimatr)

  set.seed(20261201)
  N <- 200
  cluster <- factor(rep(1:20, each = 10))
  z1 <- rnorm(N)
  z2 <- rnorm(N)
  x_exog <- rnorm(N)
  x_endog <- 0.5 * z1 + 0.3 * z2 + rnorm(N)
  y <- 1 + 2 * x_endog + 0.5 * x_exog + rnorm(N)
  dat <- data.frame(y, x_endog, x_exog, z1, z2, cluster)

  # Basic 2SLS with clusters and CR2
  iv_fit <- iv_robust(
    y ~ x_endog + x_exog | x_exog + z1 + z2,
    data = dat, 
    clusters = cluster, se_type = "CR2"
  )
  vcovCR(iv_fit)
  conf_int(iv_fit, vcov = "CR2")

  # 2SLS with fixed effects
  iv_fe <- iv_robust(
    y ~ x_endog + x_exog | x_exog + z1 + z2,
    fixed_effects = ~ cluster, 
    data = dat, 
    clusters = cluster,
    se_type = "CR2"
  )
  vcovCR(iv_fe)
  conf_int(iv_fe, vcov = "CR2")
})

clubSandwich documentation built on May 4, 2026, 9:09 a.m.