ace.train: Fit an Additive Causal Expansion model

Description Usage Arguments Value Author(s) References Examples

View source: R/main_ace.R

Description

This function fits a varying coefficient model with Gaussian process priors on the coefficients. The number of additive elements is determined by the expansion of the treatment variable.

Usage

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ace.train(y, X, Z, pi, kernel = "SE", basis = "linear", n.knots = 1,
  optimizer = "Nadam", maxiter = 1000, tol = 1e-04,
  learning_rate = 0.01, beta1 = 0.9, beta2 = 0.999, momentum = 0,
  norm.clip = (optimizer %in% c("Adam", "Nadam")), clip.at = 1,
  init.sigma = NULL, init.length_scale = 20, plot_stats = TRUE,
  verbose = TRUE)

Arguments

y

A numeric vector of the outcomes.

X

A numeric matrix of confounder variables.

Z

A vector or matrix (multivariate / tensor splines might be added in the future) Factors will be transformed to numeric using as.numeric. Hence, non-binary actors are discouraged especially when they are not ordinal.

pi

(Optional) A vector of propenbsity score that can be used for binary Z when the propensity score function is assumed to be in a different RKHS than the potential outcome function. NOTE that prediction needs to be done using newZ = (Z - pi). For refrence see Hahn et al. (2018).

kernel

A string denoting the Mercer/Covariance Kernel (default: "SE"). Options: "SE" - Squared exponential kernelwith ARD, and "Matern32" - the Matern 3/2 kernel with ARD.

basis

A string (default: "binary"/"linear" if Z is binary and "ns", natural cubic spline, for continuous or discrete Z). Options: "linear" - 1rd order polynomial, "square" - 2rd order polynomial, "cubic" - 3rd order polynomial, "B" - B-spline, and "ns" - Natural cubic spline.

n.knots

An integer denoting the number of internal knots of the spline of Z (default: 1). Ignored if the basis is not a spline.

optimizer

A string selecting the gradient optimizer (default: "Nadam"). Options: "GD" - gradient descent, "NAG" - Nesterov accelerated gradient descent, "Adam" - Adaptive moment estimation (Kingma & Ba, 2015), "Nadam" - Nesterov-accelerated Adam (Dozat, 2016).

maxiter

An integer defining the maximum number of iterations of the gradient-based empirical Bayes optimization (default: 1000).

tol

A numeric scalar defining the stopping tolerance for the gradient-based empirical Bayes optimization (default: 1e-4).

learning_rate

An integer defining the learning rate for the gradient-based empirical Bayes optimization (default: 0.01).

beta1

A numeric scalar defining the ("first moment") learning parameter for the Adam and Nadam optimizers (default: 0.9).

beta2

A numeric scalar defining the ("second moment") learning parameter for the Adam and Nadam optimizers (default: 0.999).

momentum

Momentum for the empirical Bayes optimization when using Nesterov. Equivalent to gradient descent ("GD") if momentum is 0. (default: 0.0). Ignored for Nadam and Adam optimizers.

norm.clip

A boolean scalar defining whether the gradients should be clipped based on their norm (default: TRUE if optimizer is GD or NAG, FALSE if optimizer is Adam or Nadam)

clip.at

A numeric scalar defining the maximum L2-length of the gradients (default: 1). If the Euclidian length of the gradients is above this value, they will be proportionally shrunk to this maximum. Ignored if norm.clip is FALSE.

init.sigma

A numeric scaler defining the initial value for the noise variance (default: NULL). If NULL, uses the estimated noise variance of a linear regression.

init.length_scale

A numeric scalar defining the initial value of the length sclaes of the ARD kernel (default: 20). For large values the Kernel approximates a linear model, which can be a good initial guess, especially for discrete confounders.

plot_stats

A boolean scalar to turn off the plotting of the likelihood and RMSE learning curves (default: TRUE).

verbose

A boolean scalar to turn off any text output of the function (default: FALSE).

Value

The function returns the fitted process, together with relevant training settings, as an "ace" class object. Predictions of the outcome curves as well as the marginal response (over Z) can be obtained using the accompanying "prediction" S3 method; see examples.

Author(s)

Philip Pilgerstorfer <philip at pilgerstorfer.org>

References

Examples

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library(ace)
## Example with binary treatment similar to Hill (2011)'s

set.seed(1231)
n <- 300

# generate treatment
Z <- rbinom(n, 1, 0.3)

# generate confounder and exogenous variable
X <- matrix(NaN, n, 1)
X[Z==1, ] <- rnorm(sum(Z), mean = 30,sd = 10)
X[Z==0, ] <- rnorm(n - sum(Z), mean = 20, sd = 10)
E <- runif(n) # exogenous variable
X <- data.frame(X, E)

# sort Confounder for visualizations
sort.idx <- sort(X[, 1], index.return = TRUE)$ix

# define and draw the reponse function
y_truefun <- function(x, z) {
    mat <- matrix(NaN, length(z), 1)
    mat[z==0, 1] <- matrix(72 + 3 * (x[z == 0,1] > 0) * sqrt(abs(x[z == 0, 1])), sum(z == 0), 1)
    mat[z==1, 1] <- matrix(90 + exp(0.06 * x[z == 1, 2]), sum(z == 1), 1)
    c(mat)}
y0_true <- y_truefun(X, rep(0, n))
y1_true <- y_truefun(X, rep(1, n))
Y0 <- rnorm(n, mean = y0_true, sd = 1)
Y1 <- rnorm(n, mean = y1_true, sd = 1)
Y <- Y0 * (1 - Z) + Y1 * Z

# run model
my.ace <- ace.train(Y, X, Z,
                    kernel = "SE", optimizer = "Nadam",
                    learning_rate = 0.005, maxiter = 1000)

# print (sample) average treatment effect (ATE)
my.pred <- predict(my.ace, marginal = TRUE, return_average_treatments = TRUE)

# predicted vs actual ATE
my.pred$ate
mean(y1_true - y0_true)

# plot outcome/response curves
plot_ace(my.ace, 1, marginal = FALSE)

# plot treatment curve
plot_ace(my.ace, 1, marginal = TRUE)

# Check for robustness of ATE:
robust_treatment(my.ace, n.steps=5)

## Example with continuous Z

# generate confounder and treatment (dosage)
set.seed(1234)
n2 <- 200
Xc <- data.frame(matrix(runif(2 * n2, min = 1, max = 2), n2, 2))
Zc <- rnorm(n2, Xc[,1] + exp(Xc[,1]), exp(Xc[,1]))
yc_truefun <- function(x, z) {as.matrix(20 * sin(10 * x[, 2] - 1.5)
                                        + (x[, 1] - 1.5) * abs(z^3 - 2 * z)/100)
                             }

# generate response curve
yc_true <- yc_truefun(Xc, Zc)
Yc <- rnorm(n2, mean = yc_true, sd = 2)

# train and predict model (in-sample)
my.ace <- ace.train(Yc, Xc, Zc,
                    optimizer = "Nadam",
                    learning_rate = 0.01,
                    basis = "ncs")
my.pred <- predict(my.ace)

# plot a 3D surface of the outcome response with respect to the confounder (column 1)
plot_ace(my.ace, 1, plot3D = TRUE)

# plot a 3D surface of the marginal response
plot_ace(my.ace, 1, marginal = TRUE, plot3D = TRUE)

# plot of the 2D curve with only Z using the mean for each dimension of X
plot_ace(my.ace)

mazphilip/GPspline documentation built on April 24, 2018, 3:26 a.m.