% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/stpr.R
\name{gb_stpr}
\alias{gb_stpr}
\title{Social Time Preference Rate}
\usage{
gb_stpr(years, schedule = "standard")
}
\arguments{
\item{years}{Integer vector of years from the base year (year 0 is
the base year). Must be non-negative.}

\item{schedule}{One of \code{"standard"} (default, 3.5 percent baseline),
\code{"health"} (1.5 percent baseline, used in DHSC supplementary
guidance), or \code{"catastrophic"} (3.0 percent, for projects where
catastrophic risk dominates).}
}
\value{
A numeric vector of discount rates (decimals, e.g. 0.035 for
3.5 percent), one per element of \code{years}.
}
\description{
Returns the HM Treasury Green Book Social Time Preference Rate (STPR)
for a vector of years from a base year. The schedule is kinked: the
rate steps down at 30, 75, 125, 200, and 300 years. Three variants
are supported.
}
\details{
The STPR is composed of pure time preference plus a wealth-effect
adjustment for expected per-capita consumption growth. The kink
reflects increasing uncertainty over the constituent parameters at
longer horizons.
}
\examples{
gb_stpr(0:5)
gb_stpr(c(10, 30, 31, 75, 76))
gb_stpr(c(10, 30, 31, 75, 76), schedule = "health")
}
\references{
HM Treasury (2022). The Green Book: Central Government Guidance on
Appraisal and Evaluation, Annex A6.

HM Treasury (2003). Green Book Supplementary Guidance: Discounting.
}
\seealso{
\code{\link[=gb_discount_factor]{gb_discount_factor()}}, \code{\link[=gb_discount]{gb_discount()}}, \code{\link[=gb_npv]{gb_npv()}}.

Other discounting: 
\code{\link{gb_discount}()},
\code{\link{gb_discount_factor}()},
\code{\link{gb_eanc}()},
\code{\link{gb_npv}()}
}
\concept{discounting}
