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#' Inference on the difference between unconditional and conditional Granger-causality
#'
#' \verb{Granger.inference.difference} provides bootstrap inference for the difference between
#' the Granger-causality unconditional spectrum of a time series \verb{x} (effect variable)
#' respect to a time series \verb{y} (cause variable) and the Granger-causality conditional
#' spectrum of a time series \verb{x} (effect variable) on a time series \verb{z} (conditioning variable)
#' respect to a time series \verb{y} (cause variable). It requires packages \href{https://CRAN.R-project.org/package=vars}{vars} and \href{https://CRAN.R-project.org/package=tseries}{tseries}.
#' @param x univariate time series.
#' @param y univariate time series (of the same length of \verb{x}).
#' @param z univariate time series (of the same length of \verb{x}).
#' @param ic.chosen estimation method parameter \verb{ic} to be passed to function \link[vars]{VAR} of
#' package ''vars''. Defaults to ''SC'' (Schwarz criterion). Alternatives are \verb{c(''AIC'',''HQ'',''SC'',''FPE'')}.
#' @param max.lag maximum number of lags \verb{lag.max} to be passed to function \code{\link[vars]{VAR}}.
#' Defaults to \verb{min(4, length(x) - 1)}.
#' @param plot logical; if TRUE, it returns the plot of the difference between the unconditional
#' Granger-causality spectrum from \verb{y} to \verb{x} and the conditional Granger-causality
#' spectrum from \verb{y} to \verb{x} on \verb{z} with upper and lower computed thresholds.
#' Defaults to FALSE.
#' @param type.chosen parameter \verb{type} to be passed to function \code{\link[vars]{VAR}}.
#' Defaults to \verb{''none''}. Alternatives are \verb{c(''none'',''const'',''trend'')}.
#' @param p parameter \verb{p} to be passed to function \link[vars]{VAR}.
#' It corresponds to the number of delays for unconditional GC. Defaults to 0.
#' @param p1 parameter \verb{p} to be passed to function \link[vars]{VAR}.
#' It corresponds to the number of lags of the first VAR model. Defaults to 0.
#' @param p2 parameter \verb{p} to be passed to function \link[vars]{VAR}.
#' @param nboots number of bootstrap series to be computed by function \code{\link[tseries]{tsbootstrap}}
#' of package \href{https://CRAN.R-project.org/package=tseries}{tseries}. It defaults to 1000.
#' @param conf prescribed confidence level. It defaults to 0.95.
#' @param bp_orig matrix containing previously simulated bootstrap series, having as rows
#' time points, as columns variables \verb{x} and \verb{y} (in this order). It defaults to NULL.
#' @param ts_boot boolean equal to 1 if the stationary bootstrap of
#' Politis and Romano (1994) is applied, 0 otherwise. It defaults to 1.
#' @description Inference on the difference between unconditional and conditional Granger-causality
#' spectrum is provided generating bootstrap time series by the stationary boostrap of
#' Politis and Romano (1994).
#' For computational details we refer to Ding et al. (2006) and Farne' and Montanari (2018).
#' @return \verb{frequency}: frequencies used by Fast Fourier Transform.
#' @return \verb{n}: time series length.
#' @return \verb{nboots}: number of bootstrap series used.
#' @return \verb{confidence_level}: prescribed confidence level.
#' @return \verb{stat_yes}: boolean equal to 0 if no stationary VAR
#' is estimated across bootstrap samples, 1 otherwise.
#' @return \verb{non_stationarity_rate}: percentage of estimated non-stationary VAR models (at
#' least one root larger than one) on bootstrapped \verb{x} and {y}.
#' @return \verb{non_stationarity_rate_1}: percentage of estimated non-stationary VAR models (at
#' least one root larger than one) on bootstrapped \verb{x} and {z}.
#' @return \verb{non_stationarity_rate_2}: percentage of estimated non-stationary VAR models (at
#' least one root larger than one) on bootstrapped \verb{x}, \verb{y} and {z}.
#' @return \verb{quantile_difference_inf}: lower computed quantile of the difference between the
#' Granger-causality unconditional spectrum from \verb{y} to \verb{x} and the Granger-causality
#' conditional spectrum from \verb{y} to \verb{x} on \verb{z}.
#' @return \verb{quantile_difference_sup}: upper computed quantile of the difference between the
#' Granger-causality unconditional spectrum from \verb{y} to \verb{x} and the Granger-causality
#' conditional spectrum from \verb{y} to \verb{x} on \verb{z}.
#' @return \verb{freq_inf}: frequencies at which the difference between the Granger-causality unconditional spectrum
#' from \verb{y} to \verb{x} and the Granger-causality conditional spectrum
#' from \verb{y} to \verb{x} on \verb{z} exceeds the lower computed threshold.
#' @return \verb{freq_sup}: frequencies at which the difference between the Granger-causality unconditional spectrum
#' from \verb{y} to \verb{x} and the Granger-causality conditional spectrum
#' from \verb{y} to \verb{x} on \verb{z} exceeds the upper computed threshold.
#' @return \verb{quantile_difference_max_inf}: lower computed quantile of the difference between the
#' Granger-causality unconditional spectrum from \verb{y} to \verb{x} and the Granger-causality
#' conditional spectrum from \verb{y} to \verb{x} on \verb{z} under Bonferroni correction.
#' @return \verb{quantile_difference_max_sup}: upper computed quantile of the difference between the
#' Granger-causality unconditional spectrum from \verb{y} to \verb{x} and the Granger-causality
#' conditional spectrum from \verb{y} to \verb{x} on \verb{z} under Bonferroni correction.
#' @return \verb{freq_max_inf}: frequencies at which the difference between the Granger-causality unconditional
#' spectrum from \verb{y} to \verb{x} and the Granger-causality conditional spectrum
#' from \verb{y} to \verb{x} on \verb{z} exceeds the lower computed threshold under Bonferroni correction.
#' @return \verb{freq_max_sup}: frequencies at which the difference between the Granger-causality unconditional
#' spectrum from \verb{y} to \verb{x} and the Granger-causality conditional spectrum
#' from \verb{y} to \verb{x} on \verb{z} exceeds the upper computed threshold under Bonferroni correction.
#' @return The result is returned invisibly if plot is TRUE.
#' @author Matteo Farne', Angela Montanari, \email{matteo.farne2@@unibo.it}
#' @seealso \link[vars]{VAR} and \code{\link[tseries]{tsbootstrap}}.
#' @examples
#' RealGdp.rate.ts<-euro_area_indicators[,1]
#' m3.rate.ts<-euro_area_indicators[,2]
#' hicp.rate.ts<-euro_area_indicators[,4]
#' inf_diff_pre_hicp.to.gdp_0.95<-
#' Granger.inference.difference(RealGdp.rate.ts,m3.rate.ts,hicp.rate.ts,nboots=10)
#' @references Politis D. N. and Romano J. P., (1994). ''The Stationary
#' Bootstrap''. \emph{Journal of the American Statistical Association}, 89, 1303--1313.
#' @references Ding, M., Chen, Y., Bressler, S.L., 2006. Granger Causality: Basic Theory and
#' Application to Neuroscience, Chap.17. \emph{Handbook of Time Series Analysis
#' Recent Theoretical Developments and Applications}.
#' @references Farne', M., Montanari, A., 2018. A bootstrap test to detect prominent Granger-causalities across frequencies.
#' <arXiv:1803.00374>, \emph{Submitted}.
#' @export
#' @import vars tseries
#' @importFrom graphics abline par
#' @importFrom stats coef frequency median pf qf quantile residuals spec.pgram
#' @importFrom utils install.packages installed.packages
Granger.inference.difference<-function (x, y, z, ic.chosen = "SC", max.lag = min(4, length(x) -
1), plot = F, type.chosen = "none", p=0,p1=0,p2=0,nboots = 1000, conf=0.95, bp_orig = NULL,ts_boot=1)
{
if (p==0){
mod=VAR(cbind(x,y),ic=ic.chosen,lag.max=max.lag,type.chosen)
}
if (p>0){
mod=VAR(cbind(x,y),ic=ic.chosen,lag.max=max.lag,type.chosen,p=p)
}
if (length(x) == 1) {
return("The length of x is only 1")
}
if (length(x) != length(y)) {
return("x and y do not have the same length")
}
if (max.lag > length(x) - 1) {
return("The chosen number of lags is larger than or equal to the time length")
}
##
if(!requireNamespace("vars")){
return("The packages 'vars' could not be found. Please install it to
proceed.")
}
if(!requireNamespace("tseries")){
return("The packages 'tseries' could not be found. Please install it to
proceed.")
}
requireNamespace("vars")
requireNamespace("tseries")
if (p1==0){
model1=VAR(cbind(x,z),ic=ic.chosen,lag.max=max.lag,type.chosen)
}
if (p1>0){
model1=VAR(cbind(x,z),p=p1,type.chosen)
}
if (p2==0){
model2=VAR(cbind(x,y,z),ic=ic.chosen,lag.max=max.lag,type.chosen)
}
if (p2>0){
model2=VAR(cbind(x,y,z),p=p2,type.chosen)
}
if(ts_boot==1){
if (is.array(bp_orig) != TRUE) {
x_bp <- tsbootstrap(x, nb = nboots)
y_bp <- tsbootstrap(y, nb = nboots)
z_bp <- tsbootstrap(z, nb = nboots)
}
if (is.array(bp_orig) == TRUE) {
x_bp <- bp_orig[, , 1]
y_bp <- bp_orig[, , 2]
z_bp <- bp_orig[, , 3]
}
freq.good = spec.pgram(y, plot = F)$freq/frequency(y)
no_freq=0;
}
test_stationarity <- vector("numeric", nboots)
cause_y.to.x.on.z_bp <- array(0, dim = c(nboots, length(freq.good)))
cause_y.to.x_bp <- array(0, dim = c(nboots, length(freq.good)))
test_stationarity_1 <- vector("numeric", nboots)
test_stationarity_2 <- vector("numeric", nboots)
cause_diff_y.to.x.on.z_bp <- array(0, dim = c(nboots, length(freq.good)))
cause_diff_y.to.x.on.z_bp_signed <- array(0, dim = c(nboots, length(freq.good)))
top_diff_y.to.x.on.z_bp_signed <- vector("numeric", nboots)
for (w in 1:nboots) {
xy_mat<-as.data.frame(cbind(x_bp[, w], y_bp[, w]));
colnames(xy_mat)<-c("x_bp","y_bp")
if(p>0){
mod_bp<-VAR(xy_mat, type.chosen,p=mod$p)
G.xy <- Granger.unconditional(xy_mat[, 1], xy_mat[, 2], plot=F, type.chosen, p=mod$p)
}
if(p==0){
mod_bp<-VAR(xy_mat, ic=ic.chosen,
lag.max=max.lag, type.chosen)
G.xy <- Granger.unconditional(xy_mat[, 1], xy_mat[, 2], ic.chosen,
max.lag, F, type.chosen)
}
cause_y.to.x_bp[w, ] <- G.xy$Unconditional_causality_y.to.x
if (length(which(abs(G.xy$roots) >= 1)) > 0) {
test_stationarity[w] = 1}
if(ts_boot==1){
xz_mat<-as.data.frame(cbind(x_bp[, w], z_bp[, w]));
xyz_mat<-as.data.frame(cbind(x_bp[, w],y_bp[, w], z_bp[, w]));
colnames(xz_mat)<-c("x_bp","z_bp")
colnames(xyz_mat)<-c("x_bp","y_bp","z_bp")
if(p1>0 && p2>0){
model1_bp<-VAR(xz_mat, type.chosen,p=model1$p)
model2_bp<-VAR(xyz_mat, type.chosen,p=model2$p)
GG.xy <- Granger.conditional(xyz_mat[, 1], xyz_mat[, 2], xyz_mat[, 3], plot=F, type.chosen, p1=model1$p,p2=model2$p)
}
if(p1==0 && p2==0){
model1_bp<-VAR(xz_mat, ic=ic.chosen,
lag.max=max.lag, type.chosen)
model2_bp<-VAR(xyz_mat, ic=ic.chosen,
lag.max=max.lag, type.chosen)
GG.xy <- Granger.conditional(xyz_mat[, 1], xyz_mat[, 2], xyz_mat[, 3], ic.chosen,
max.lag, F, type.chosen)
}
}
#if(is.na(GG.xy)[1]==F){
cause_y.to.x.on.z_bp[w, ] <- GG.xy$Conditional_causality_y.to.x.on.z
#}
if (length(which(abs(GG.xy$roots_1) >= 1)) > 0) {
test_stationarity_1[w] = 1
}
if (length(which(abs(GG.xy$roots_2) >= 1)) > 0) {
test_stationarity_2[w] = 1
}
cause_diff_y.to.x.on.z_bp_signed[w,]<-(cause_y.to.x_bp[w, ] - cause_y.to.x.on.z_bp[w,])
top_diff_y.to.x.on.z_bp_signed[w] <- median((cause_diff_y.to.x.on.z_bp_signed[w, ]))
}
stationary <- intersect(which(test_stationarity == 0), intersect(which(test_stationarity_1 ==
0), which(test_stationarity_2 == 0)))
non_stationarity_rate <- sum(test_stationarity)/nboots
non_stationarity_rate_1 <- sum(test_stationarity_1)/nboots
non_stationarity_rate_2 <- sum(test_stationarity_2)/nboots
stat_rate<-length(stationary)/nboots
if (length(stationary)>=nboots/nboots){
stat_yes=1;
n <- G.xy$n
GG_x_orig <- Granger.unconditional(x, y, ic.chosen, max.lag,
F)$Unconditional_causality_y.to.x
GG_x.on.z <- Granger.conditional(x, y, z, ic.chosen, max.lag,
F)$Conditional_causality_y.to.x.on.z
q_diff_x_inf <- quantile(top_diff_y.to.x.on.z_bp_signed[stationary],(1-conf)/2)
q_diff_x_sup <- quantile(top_diff_y.to.x.on.z_bp_signed[stationary],1-(1-conf)/2)
diff_GG <- (GG_x_orig - GG_x.on.z)
signif_diff_x_sup <- which(diff_GG > q_diff_x_sup)
signif_diff_x_inf <- which(diff_GG < q_diff_x_inf)
conf_bonf<-(1-conf)/length(freq.good)
q_diff_max_inf <- quantile(top_diff_y.to.x.on.z_bp_signed[stationary],(1-conf_bonf)/2)
q_diff_max_sup <- quantile(top_diff_y.to.x.on.z_bp_signed[stationary],1-(1-conf_bonf)/2)
diff_GG <- (GG_x_orig - GG_x.on.z)
signif_diff_max_sup <- which(diff_GG > q_diff_max_sup)
signif_diff_max_inf <- which(diff_GG < q_diff_max_inf)
GG <- list(freq.good, n, nboots, conf, stat_yes, non_stationarity_rate, non_stationarity_rate_1, non_stationarity_rate_2,
q_diff_x_sup, q_diff_x_inf, freq.good[signif_diff_x_sup], freq.good[signif_diff_x_inf],q_diff_max_sup, q_diff_max_inf, freq.good[signif_diff_max_sup],freq.good[signif_diff_max_inf])
names(GG) <- c("frequency", "n", "nboots", "confidence_level", "stat_yes", "non_stationarity_rate", "non_stationarity_rate_1", "non_stationarity_rate_2",
"quantile_difference_sup", "quantile_difference_inf", "freq_sup","freq_inf","quantile_difference_max_sup", "quantile_difference_max_inf", "freq_max_sup","freq_max_inf")
}
if (length(stationary)<nboots/nboots){
stat_yes=0;
stat_rate=0;
no_freq=0;
GG<-list(stat_yes,stat_rate,no_freq)
names(GG)<-c("stat_yes","stat_rate","no_freq")
}
if (plot == F) {
return(GG)
}
if (plot == T) {
par(mfrow = c(1, 1))
plot(freq.good, diff_GG, type = "l", main = "Difference Unconditional/Conditional")
abline(h = q_diff_x_sup)
}
}
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