crossval {ddml}

Estimator of the Mean Squared Prediction Error using Cross-Validation.

Description

Estimator of the mean squared prediction error of different learners using cross-validation.

Usage

crossval(
  y,
  X,
  Z = NULL,
  learners,
  cv_folds = 5,
  cv_subsamples = NULL,
  silent = FALSE,
  progress = NULL
)

Arguments

y

The outcome variable.

X

A (sparse) matrix of predictive variables.

Z

Optional additional (sparse) matrix of predictive variables.

learners

learners is a list of lists, each containing four named elements:

• fun The base learner function. The function must be such that it predicts a named input y using a named input X.

• args Optional arguments to be passed to fun.

• assign_X An optional vector of column indices corresponding to variables in X that are passed to the base learner.

• assign_Z An optional vector of column indices corresponding to variables in Z that are passed to the base learner.

Omission of the args element results in default arguments being used in fun. Omission of assign_X (and/or assign_Z) results in inclusion of all predictive variables in X (and/or Z).

cv_folds

Number of folds used for cross-validation.

cv_subsamples

List of vectors with sample indices for cross-validation.

silent

Boolean to silence estimation updates.

progress

String to print before learner and cv fold progress.

Value

crossval returns a list containing the following components:

mspe

A vector of MSPE estimates, each corresponding to a base learners (in chronological order).

oos_resid

A matrix of out-of-sample prediction errors, each column corresponding to a base learners (in chronological order).

cv_subsamples

Pass-through of cv_subsamples. See above.

See Also

Other utilities: crosspred(), shortstacking()

Examples

# Construct variables from the included Angrist & Evans (1998) data
y = AE98[, "worked"]
X = AE98[, c("morekids", "age","agefst","black","hisp","othrace","educ")]

# Compare ols, lasso, and ridge using 4-fold cross-validation
cv_res <- crossval(y, X,
                   learners = list(list(fun = ols),
                                   list(fun = mdl_glmnet),
                                   list(fun = mdl_glmnet,
                                        args = list(alpha = 0))),
                   cv_folds = 4,
                   silent = TRUE)
cv_res$mspe