conformalCf: Conformal inference for counterfactuals

In mingzhang-yin/Conformal-sensitivity-analysis: Conformal inference of counterfactuals and individual treatment effects

Conformal inference for counterfactuals

Description

conformalCf computes intervals for counterfactuals or outcomes with ignorable missing values in general. It supports both split conformal inference and CV+, including weighted Jackknife+ as a special case. For each type, it supports both conformalized quantile regression (CQR) and standard conformal inference based on conditional mean regression.

Usage

conformalCf(
  X,
  Y,
  estimand = c("unconditional", "nonmissing", "missing"),
  type = c("CQR", "mean"),
  side = c("two", "above", "below"),
  quantiles = NULL,
  outfun = NULL,
  outparams = list(),
  psfun = NULL,
  psparams = list(),
  useCV = FALSE,
  trainprop = 0.75,
  nfolds = 10
)

Arguments

X	covariates.
Y	outcome vector with missing values encoded as NA. See Details.
estimand	a string that takes values in {"unconditional", "nonmissing", "missing"}. See Details.
type	a string that takes values in {"CQR", "mean"}.
side	a string that takes values in {"two", "above", "below"}. See Details.
quantiles	a scalar or a vector of length 2 depending on side. Used only when type = "CQR". See Details.
outfun	a function that models the conditional mean or quantiles, or a valid string. The default is random forest when type = "mean" and quantile random forest when type = "CQR". See Details.
outparams	a list of other parameters to be passed into outfun.
psfun	a function that models the missing mechanism (probability of missing given X), or a valid string. The default is "Boosting". See Details.
psparams	a list of other parameters to be passed into psfun.
useCV	FALSE for split conformal inference and TRUE for CV+.
trainprop	proportion of units for training outfun. The default if 75%. Used only when useCV = FALSE.
nfolds	number of folds. The default is 10. Used only when useCV = TRUE.

Details

The outcome Y must comprise both observed values and missing values encoded as NA. The missing values are used to estimate the propensity score P(missing | X).

estimand controls the type of coverage to be guaranteed:

• (Default) when estimand = "unconditional", the interval has P(Y \in \hat{C}(X))\ge 1 - \alpha.

• When estimand = "nonmissing", the interval has P(Y \in \hat{C}(X) | nonmissing) \ge 1 - \alpha.

• When estimand = "missing", the interval has P(Y \in \hat{C}(X) | missing) \ge 1 - \alpha.

When side = "above", intervals are of form [-Inf, a(x)] and when side = "below" the intervals are of form [a(x), Inf].

outfun can be a valid string, including

• "RF" for random forest that predicts the conditional mean, a wrapper built on randomForest package. Used when type = "mean".

• "quantRF" for quantile random forest that predicts the conditional quantiles, a wrapper built on grf package. Used when type = "CQR".

• "Boosting" for gradient boosting that predicts the conditional mean, a wrapper built on gbm package. Used when type = "mean".

• "quantBoosting" for quantile gradient boosting that predicts the conditional quantiles, a wrapper built on gbm package. Used when type = "CQR".

• "BART" for gradient boosting that predicts the conditional mean, a wrapper built on bartMachine package. Used when type = "mean".

• "quantBART" for quantile gradient boosting that predicts the conditional quantiles, a wrapper built on bartMachine package. Used when type = "CQR".

or a function object whose input must include, but not limited to

• Y for outcome in the training data.

• X for covariates in the training data.

• Xtest for covariates in the testing data.

When type = "CQR", outfun should also include an argument quantiles that is either a vector of length 2 or a scalar, depending on the argument side. The output of outfun must be a matrix with two columns giving the conditional quantile estimates when quantiles is a vector of length 2; otherwise, it must be a vector giving the conditional quantile estimate or conditional mean estimate. Other optional arguments can be passed into outfun through outparams.

psfun can be a valid string, including

• "RF" for random forest that predicts the propensity score, a wrapper built on randomForest package. Used when type = "mean".

• "Boosting" for gradient boosting that predicts the propensity score, a wrapper built on gbm package. Used when type = "mean".

or a function object whose input must include, but not limited to

• Y for treatment assignment, a binary vector, in the training data.

• X for covariates in the training data.

• Xtest for covariates in the testing data.

The output of psfun must be a vector of predicted probabilities. Other optional arguments can be passed into psfun through psparams.

Value

a conformalSplit object when useCV = FALSE or a conformalCV object

See Also

conformal, conformalIte

Examples

# Generate data from a linear model
set.seed(1)
n <- 1000
d <- 5
X <- matrix(rnorm(n * d), nrow = n)
beta <- rep(1, 5)
Y <- X %*% beta + rnorm(n)

# Generate missing indicators
missing_prob <- pnorm(X[, 1])
if_missing <- missing_prob < runif(n)
Y[if_missing] <- NA

# Generate testing data
ntest <- 5
Xtest <- matrix(rnorm(ntest * d), nrow = ntest)

# Run weighted split CQR
obj <- conformalCf(X, Y, type = "CQR", quantiles = c(0.05, 0.95),
                   outfun = "quantRF", useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

# Run weighted standard conformal inference
obj <- conformalCf(X, Y, type = "mean",
                   outfun = "RF", useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

# Run one-sided weighted split CQR
obj1 <- conformalCf(X, Y, type = "CQR", side = "above",
                    quantiles = 0.95, outfun = "quantRF", useCV = FALSE)
predict(obj1, Xtest, alpha = 0.1)
obj2 <- conformalCf(X, Y, type = "CQR", side = "below",
                    quantiles = 0.05, outfun = "quantRF", useCV = FALSE)
predict(obj2, Xtest, alpha = 0.1)

# Run split CQR with a self-defined quantile random forest
# Y, X, Xtest, quantiles should be included in the inputs
quantRF <- function(Y, X, Xtest, quantiles, ...){
    fit <- grf::quantile_forest(X, Y, quantiles = quantiles, ...)
    res <- predict(fit, Xtest, quantiles = quantiles)
    if (length(quantiles) == 1){
        res <- as.numeric(res)
    } else {
        res <- as.matrix(res)
    }
    return(res)
}
obj <- conformalCf(X, Y, type = "CQR", quantiles = c(0.05, 0.95),
                   outfun = quantRF, useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

# Run standard split conformal inference with a self-defined linear regression
# Y, X, Xtest should be included in the inputs
linearReg <- function(Y, X, Xtest){
    X <- as.data.frame(X)
    Xtest <- as.data.frame(Xtest)
    data <- data.frame(Y = Y, X)
    fit <- lm(Y ~ ., data = data)
    as.numeric(predict(fit, Xtest))
}
obj <- conformalCf(X, Y, type = "mean",
                   outfun = linearReg, useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

# Run split CQR with a built-in psfun
# Y, X, Xtest, should be included in the inputs
obj <- conformalCf(X, Y, type = "CQR", quantiles = c(0.05, 0.95),
                   outfun = "quantRF", psfun = "RF", useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

# Run split CQR with a self-defined function to estimate propensity scores
# Y, X, Xtest, should be included in the inputs
logitReg <- function(Y, X, Xtest, ...){
    X <- as.data.frame(X)
    Xtest <- as.data.frame(Xtest)
    data <- data.frame(Y = Y, X)
    fit <- glm(Y ~ ., data = data, family = "binomial", ...)
    as.numeric(predict(fit, Xtest, type = "response"))
}
obj <- conformalCf(X, Y, type = "CQR", quantiles = c(0.05, 0.95),
                   outfun = "quantRF", psfun = logitReg, useCV = FALSE)
predict(obj, Xtest, alpha = 0.1)

mingzhang-yin/Conformal-sensitivity-analysis documentation built on Jan. 5, 2024, 8:14 a.m.