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predict.spdur.R
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predict.spdur.R
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#' Predict methods for spdur Objects
#'
#' \code{predict} and related methods for class ``\code{spdur}''.
#'
#' @method predict spdur
#'
#' @param object Object of class ``\code{spdur}''.
#' @param newdata Optional data for which to calculate fitted values, defaults to
#' training data.
#' @param type Quantity of interest to calculate. Default conditional hazard,
#' i.e. conditioned on observed survival up to time \code{t}.
#' See below for list of values. For \code{residuals}, the type of residual to
#' calculate
#' @param truncate For conditional hazard, truncate values greater than 1.
#' @param na.action Function determining what should be done with missing values
#' in newdata. The default is to predict NA (\code{na.exclude}).
#' @param \dots not used, for compatibility with generic function.
#'
#' @details
#' Calculates various types of probabilities, where ``conditional'' is used in
#' reference to conditioning on the observed survival time of a spell up to
#' time \eqn{t}, in addition to conditioning on any variables included in the
#' model (which is always done). Valid values for the \code{type} option
#' include:
#' \itemize{
#' \item ``conditional risk'': \eqn{Pr(Cure=0|Z\gamma, T>t)}{Pr(Cure=0|Z*gamma, T>t)}
#' \item ``conditional cure'': \eqn{Pr(Cure=1|Z\gamma, T>t)}{Pr(Cure=1|Z*gamma, T>t)}
#' \item ``hazard'': \eqn{Pr(T=t|T>t, C=0, X\beta) * Pr(Cure=0|Z\gamma)}{Pr(T=t|T>t, C=0, X*beta) * Pr(Cure=0|Z*gamma)}
#' \item ``failure'': \eqn{Pr(T=t|T>t-1, C=0, X\beta) * Pr(Cure=0|Z\gamma)}{Pr(T=t|T>t-1, C=0, X*beta) * Pr(Cure=0|Z*gamma)}
#' \item ``unconditional risk'': \eqn{Pr(Cure=0|Z\gamma)}{Pr(Cure=0|Z*gamma)}
#' \item ``unconditional cure'': \eqn{Pr(Cure=1|Z\gamma)}{Pr(Cure=1|Z*gamma)}
#' \item ``conditional hazard'' or ``response'': \eqn{Pr(T=t|T>t, C=0, X\beta) * Pr(Cure=0|Z\gamma, T>t)}{Pr(T=t|T>t, C=0, X*beta) * Pr(Cure=0|Z*gamma, T>t)}
#' \item ``conditional failure'': \eqn{Pr(T=t|T>t-1, C=0, X\beta) * Pr(Cure=0|Z\gamma, T>t)}{Pr(T=t|T>t-1, C=0, X*beta) * Pr(Cure=0|Z*gamma, T>t)}
#' }
#' The vector \eqn{Z\gamma}{Z*gamma} indicates the cure/at risk equation
#' covariate vector, while \eqn{X\beta}{X*beta} indicates the duration equation
#' covariate vector.
#'
#' @return
#' Returns a data frame with 1 column corresponding to \code{type}, in the same
#' order as the data frame used to estimate \code{object}.
#'
#' @note See \code{\link{forecast.spdur}} for producing forecasts when future
#' covariate values are unknown.
#'
#' @examples
#' # get model estimates
#' data(model.coups)
#' ch <- predict(model.coups)
#'
#' @export
predict.spdur <- function(object, newdata = NULL, type = "response",
truncate = TRUE, na.action = na.exclude, ...) {
# Input validation
type_choices <- c('response', 'conditional risk', 'conditional cure', 'hazard', 'failure',
'unconditional risk', 'unconditional cure',
'conditional hazard', 'conditional failure')
if (!type %in% type_choices) stop('unknown statistic')
# minimum value for P, to avoid divide by 0 errors
p_min <- 1e-16
# Get model frames
if(is.null(newdata)) {
# From object
mf.dur <- object$mf.dur
mf.risk <- object$mf.risk
Y <- object$Y
} else {
# From provided data
fmla.dur <- terms(object$mf.dur)
fmla.risk <- terms(object$mf.risk)
vars <- unique(c(all.vars(fmla.dur), all.vars(fmla.risk)))
last <- attr(object$Y, "last")
t.0 <- attr(object$Y, "t.0")
vars <- c(vars, last, t.0)
# # hack to fix bug when data are complete (missing model na.action)
# if (all(complete.cases(newdata[, vars]))==FALSE) {
# na.action <- paste0("na.", class(na.action(object)))
# if (na.action=="na.NULL") na.action <- options("na.action")[[1]]
# df <- do.call(na.action, list(newdata[, vars]))
# } else {
# df <- newdata[, vars]
# }
df <- do.call(na.action, list(newdata[, vars]))
if (any(is.na(df))) stop("missing values in newdata (na.pass is not supported)")
mf.dur <- model.frame(formula=fmla.dur, data=df)
mf.risk <- model.frame(formula=fmla.risk, data=df)
lhb <- model.response(mf.dur)
lhg <- model.response(mf.risk)
Y <- cbind(atrisk=lhg, duration=lhb, last=df[, last], t.0=df[, t.0])
}
distr <- object$distr
# Design matrices
X <- model.matrix(attr(mf.dur, 'terms'), data=mf.dur)
Z <- model.matrix(attr(mf.risk, 'terms'), data=mf.risk)
# DV
ti <- Y[, 2] # Time at current period
t0 <- Y[, 4] # Time at previous period
# coefficients
coeff.b <- coef(object, model = "duration")
coeff.g <- coef(object, model = "risk")
coeff.a <- coef(object, model = "distr")
alpha <- exp(-coeff.a)
lambda <- pmax(p_min, exp(-X %*% coeff.b)) # raise 0 to slightly above 0 to prevent division by 0 below
## Start with actual prediction
# Unconditional cure/atrisk rate
atrisk <- plogis(Z %*% coeff.g)
cure <- 1 - atrisk
if (type=='unconditional cure') res <- cure
if (type=='unconditional risk') res <- atrisk
# S(T)
if (distr=='weibull') {
st <- exp(-(lambda * ti)^alpha)
s0 <- exp(-(lambda * t0)^alpha)
}
if (distr=='loglog') {
st <- 1/(1+(lambda * ti)^alpha)
s0 <- 1/(1+(lambda * t0)^alpha)
}
# Conditional cure/atrisk rate
cure.t <- cure / pmax(p_min, (st + cure * (1 - st))) # pmax to avoid dividing it by 0
atrisk.t <- 1 - cure.t
if (type=='conditional cure') res <- cure.t
if (type=='conditional risk') res <- atrisk.t
# Calculate f(t)
if (distr=='weibull') {
ft <- lambda * alpha * (lambda * ti)^(alpha-1) * exp(-(lambda * ti)^alpha)
}
if (distr=='loglog') {
ft <- (lambda * alpha * (lambda * ti)^(alpha-1)) / ((1 + (lambda * ti)^alpha)^2)
}
if (type=='failure') {
# Pr(T=t | (T > t-1, not cured)) * Pr(not cured)
res <- atrisk * ft / pmax(p_min, (cure + atrisk * s0))
}
if (type=='hazard') {
# Pr(T=t | (T > t, not cured)) * Pr(not cured)
res <- atrisk * ft / pmax(p_min, (cure + atrisk * st))
}
if (type=='conditional failure') {
# Pr(T=t | (T > t-1, not cured)) * Pr(not cured | T > t)
res <- atrisk.t * ft / pmax(p_min, (cure.t + atrisk.t * s0))
}
if (type=='conditional hazard' | type=="response") {
# Pr(T=t | (T > t, not cured)) * Pr(not cured | T > t)
res <- atrisk.t * ft / pmax(p_min, (cure.t + atrisk.t * st))
}
# Sometimes h(t) can > 1, truncate these values?
if (truncate) res <- ifelse(res>1, 1, res)
# Process na.action in original model
if (missing(newdata)) {
res <- napredict(object$na.action, res)
} else {
res <- napredict(attr(df, "na.action"), res)
}
return(as.numeric(res))
}
#' @rdname predict.spdur
#'
#' @method fitted spdur
#'
#' @examples
#' head(fitted(model.coups))
#'
#' @export
fitted.spdur <- function(object, ...)
{
res <- predict(object, type = "conditional hazard")
return(res)
}
#' @rdname predict.spdur
#'
#' @method residuals spdur
#'
#' @examples
#' head(residuals(model.coups))
#'
#' @export
residuals.spdur <- function(object, type = c("response"), ...)
{
# look into adding deviance and pearson residuals
ch <- predict(object, type = "conditional hazard")
# pad Y with NA's in appropriate places; can use either napredict or naresid for this
res <- naresid(object$na.action, object$Y[, "fail"]) - ch
res
}