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#' Weibull Regression
#'
#' Proportional hazards model with baseline hazard(s) from the Weibull family
#' of distributions. Allows for stratification with different scale and shape
#' in each stratum, and left truncated and right censored data.
#'
#' The parameterization is the same as in \code{\link{coxreg}} and
#' \code{\link[survival]{coxph}}, but different from the one used by
#' \code{\link[survival]{survreg}}. The model is \deqn{h(t; a, b, \beta, z) =
#' (a/b) (t/b)^{a-1} exp(z\beta)}{% h(t; a, b, beta, z) = (a/b) (t/b)^(a-1)
#' exp(z beta)} This is in correspondence with \code{\link{Weibull}}. To
#' compare regression coefficients with those from \code{survreg} you need to
#' divide by estimated shape (\eqn{\hat{a}}{a}) and change sign. The p-values
#' and test statistics are however the same, with one exception; the score test
#' is done at maximized scale and shape in \code{weibreg}.
#'
#' This model is a Weibull distribution with shape parameter \eqn{a} and scale
#' parameter \eqn{b \exp(-z\beta / a)}{b exp(-z beta / a)}
#'
#' @param formula a formula object, with the response on the left of a ~
#' operator, and the terms on the right. The response must be a survival
#' object as returned by the Surv function.
#' @param data a data.frame in which to interpret the variables named in the
#' formula.
#' @param na.action a missing-data filter function, applied to the model.frame,
#' after any subset argument has been used. Default is
#' \code{options()$na.action}.
#' @param init vector of initial values of the iteration. Default initial
#' value is zero for all variables.
#' @param shape If positive, the shape parameter is fixed at that value (in
#' each stratum). If zero or negative, the shape parameter is estimated. If
#' more than one stratum is present in data, each stratum gets its own
#' estimate.
#' @param control a list with components \code{eps} (convergence criterion),
#' \code{maxiter} (maximum number of iterations), and \code{silent} (logical,
#' controlling amount of output). You can change any component without mention
#' the other(s).
#' @param singular.ok Not used.
#' @param model Not used.
#' @param x Return the design matrix in the model object?
#' @param y Return the response in the model object?
#' @param center Deprecated, and not used. Will be removed in the future.
#' @return A list of class \code{c("weibreg", "coxreg")} with components
#' \item{coefficients}{Fitted parameter estimates.} \item{var}{Covariance
#' matrix of the estimates.} \item{loglik}{Vector of length two; first
#' component is the value at the initial parameter values, the second componet
#' is the maximized value.} \item{score}{The score test statistic (at the
#' initial value).} \item{linear.predictors}{The estimated linear predictors.}
#' \item{means}{Means of the columns of the design matrix.}
#' \item{w.means}{Weighted (against exposure time) means of covariates;
#' weighted relative frequencies of levels of factors.} \item{n}{Number of
#' spells in indata (possibly after removal of cases with NA's).}
#' \item{events}{Number of events in data.} \item{terms}{Used by extractor
#' functions.} \item{assign}{Used by extractor functions.} %
#' \item{wald.test}{The Wald test statistic (at the initial value).}
#' \item{y}{The Surv vector.} \item{isF}{Logical vector indicating the
#' covariates that are factors.} \item{covars}{The covariates.}
#' \item{ttr}{Total Time at Risk.} \item{levels}{List of levels of factors.}
#' \item{formula}{The calling formula.} \item{call}{The call.}
#' \item{method}{The method.} \item{convergence}{Did the optimization
#' converge?} \item{fail}{Did the optimization fail? (Is \code{NULL} if not).}
#' \item{pfixed}{TRUE if shape was fixed in the estimation.}
#' @note This function is not maintained, and may behave in unpredictable ways.
#' Use \code{\link{phreg}} with \code{dist = "weibull"} (the default) instead!
#' Will soon be declared deprecated.
#' @section Warning: The print method \code{\link{print.weibreg}} doesn't work
#' if threeway or higher order interactions are present.
#'
#' Note further that covariates are internally centered, if \code{center =
#' TRUE}, by this function, and this is not corrected for in the output. This
#' affects the estimate of \eqn{\log(scale)}{log(scale)}, but nothing else. If
#' you don't like this, set \code{center = FALSE}.
#' @author Göran Broström
#' @seealso \code{\link{phreg}}, \code{\link{coxreg}},
#' \code{\link{print.weibreg}}
#' @keywords survival regression
#' @examples
#'
#' dat <- data.frame(time = c(4, 3, 1, 1, 2, 2, 3),
#' status = c(1, 1, 1, 0, 1, 1, 0),
#' x = c(0, 2, 1, 1, 1, 0, 0),
#' sex = c(0, 0, 0, 0, 1, 1, 1))
#' weibreg( Surv(time, status) ~ x + strata(sex), data = dat) #stratified model
#'
#' @export weibreg
weibreg <-
function (formula = formula(data),
data = parent.frame(),
na.action = getOption("na.action"),
init,
shape = 0, ## Means shape is estimated, ie true Weibull; > 0 fixed!
control = list(eps = 1e-4, maxiter = 10, trace = FALSE),
singular.ok = TRUE,
model = FALSE,
x = FALSE,
y = TRUE,
center = TRUE)
{
pfixed <- (shape > 0)
call <- match.call()
m <- match.call(expand.dots = FALSE)
temp <- c("", "formula", "data", "na.action")
m <- m[match(temp, names(m), nomatch = 0)]
special <- "strata"
Terms <- if (missing(data))
terms(formula, special)
else terms(formula, special, data = data)
m$formula <- Terms
m[[1]] <- as.name("model.frame")
m <- eval(m, parent.frame())
Y <- model.extract(m, "response")
if (!inherits(Y, "Surv"))
stop("Response must be a survival object")
weights <- model.extract(m, "weights")
offset <- attr(Terms, "offset")
tt <- length(offset)
offset <- if (tt == 0)
rep(0, nrow(Y))
else if (tt == 1)
m[[offset]]
else {
ff <- m[[offset[1]]]
for (i in 2:tt) ff <- ff + m[[offset[i]]]
ff
}
attr(Terms, "intercept") <- 1
strats <- attr(Terms, "specials")$strata
dropx <- NULL
if (length(strats)) {
temp <- survival::untangle.specials(Terms, "strata", 1)
dropx <- c(dropx, temp$terms)
if (length(temp$vars) == 1)
strata.keep <- m[[temp$vars]]
else strata.keep <- survival::strata(m[, temp$vars], shortlabel = TRUE)
strats <- as.numeric(strata.keep)
}
if (length(dropx))
newTerms <- Terms[-dropx]
else newTerms <- Terms
X <- model.matrix(newTerms, m)
assign <- lapply(survival::attrassign(X, newTerms)[-1], function(x) x - 1)
X <- X[, -1, drop = FALSE]
ncov <- NCOL(X)
#########################################
if (ncov){
if (length(dropx)){
covars <- names(m)[-c(1, (dropx + 1))]
}else{
covars <- names(m)[-1]
}
isF <- logical(length(covars))
for (i in 1:length(covars)){
if (length(dropx)){
isF[i] <- ( is.factor(m[, -(dropx + 1)][, (i + 1)]) ||
is.logical(m[, -(dropx + 1)][, (i + 1)]) )
}else{
isF[i] <- ( is.factor(m[, (i + 1)]) ||
is.logical(m[, (i + 1)]) )
}
}
if (ant.fak <- sum(isF)){
levels <- list()
index <- 0
for ( i in 1:length(covars) ){
if (isF[i]){
index <- index + 1
if (length(dropx)){
levels[[i]] <- levels(m[, -(dropx + 1)][, (i + 1)])
}else{
levels[[i]] <- levels(m[, (i + 1)])
}
}else{
##cat("NULL level no ", i, "\n")
levels[[i]] <- NULL
}
}
}else{
levels <- NULL
}
}
##########################################
type <- attr(Y, "type")
if (type != "right" && type != "counting")
stop(paste("This model doesn't support \"", type, "\" survival data",
sep = ""))
if (NCOL(Y) == 2){
Y <- cbind(numeric(NROW(Y)), Y)
}
n.events <- sum(Y[, 3] != 0)
if (n.events == 0) stop("No events; no sense in continuing!")
if (missing(init))
init <- NULL
if (is.list(control)){
if (is.null(control$eps)) control$eps <- 1e-4
if (is.null(control$maxiter)) control$maxiter <- 10
if (is.null(control$trace)) control$trace <- FALSE
}else{
stop("control must be a list")
}
fit <- weibreg.fit(X,
Y,
strats,
offset,
init,
shape,
control,
center)
if (ncov){
fit$linear.predictors <- offset + X %*% fit$coefficients[1:ncov]
fit$means <- apply(X, 2, mean)
}else{
fit$linear.predictors <- NULL
fit$means <- NULL
}
##score <- exp(lp)
if (!fit$fail){
fit$fail <- NULL
}else{
out <- paste("Singular hessian; suspicious variable No. ",
as.character(fit$fail), ":\n",
names(coefficients)[fit$fail], " = ",
as.character(fit$value),
"\nTry running with fixed shape", sep = "")
stop(out)
}
fit$convergence <- as.logical(fit$conver)
fit$conver <- NULL ## Ugly!
###########################################################################
## Crap dealt with ......
if (is.character(fit)) {
fit <- list(fail = fit)
class(fit) <- "mlreg"
}
else if (is.null(fit$fail)){
if (!is.null(fit$coef) && any(is.na(fit$coef))) {
vars <- (1:length(fit$coef))[is.na(fit$coef)]
msg <- paste("X matrix deemed to be singular; variable",
paste(vars, collapse = " "))
if (singular.ok)
warning(msg)
else stop(msg)
}
fit$n <- nrow(Y)
fit$terms <- Terms
fit$assign <- assign
if (FALSE){ ## Out-commented...(why?)
if (length(fit$coef) && is.null(fit$wald.test)) {
nabeta <- !is.na(fit$coef)
if (is.null(init))
temp <- fit$coef[nabeta]
else temp <- (fit$coef - init)[nabeta]
##fit$wald.test <-
##survival:::coxph.wtest(fit$var[nabeta, nabeta],
## temp, control$toler.chol)$test
}
}
na.action <- attr(m, "na.action")
if (length(na.action))
fit$na.action <- na.action
if (model)
fit$model <- m
if (x) {
fit$x <- X
if (length(strats))
fit$strata <- strata.keep
}
if (y)
fit$y <- Y
}
##if (!is.null(weights) && any(weights != 1))
## fit$weights <- weights
##########################################
s.wght <- (Y[, 2] - Y[, 1])## * weights
fit$ttr <- sum(s.wght)
if (ncov){
fit$isF <- isF
fit$covars <- covars
fit$w.means <- list()
for (i in 1:length(fit$covars)){
nam <- fit$covars[i]
col.m <- which(nam == names(m))
if (isF[i]){
n.lev <- length(levels[[i]])
fit$w.means[[i]] <- numeric(n.lev)
for (j in 1:n.lev){
who <- m[, col.m] == levels[[i]][j]
fit$w.means[[i]][j] <-
sum( s.wght[who] ) / fit$ttr ## * 100, if in per cent
}
}else{
fit$w.means[[i]] <- sum(s.wght * m[, col.m]) / fit$ttr
}
}
fit$means <- colMeans(X)
}
##########################################
fit$ttr <- sum(s.wght)
##names(fit$coefficients) <- coef.names
fit$levels <- levels
fit$formula <- formula(Terms)
fit$call <- call
fit$n.events <- n.events
##class(fit) <- c("weibreg", "coxreg", "coxph")
class(fit) <- c("weibreg", "phreg")
fit$pfixed <- pfixed
fit
}
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