Creates a SURVIVAL object with a Gompertz distribution.
Value
a SURVIVAL object of the Gompertz distribution family. See the
documentation of s_factory for the methods available for SURVIVAL objects
Parameters
To create a Gompertz survival object the following options are available:
scale and shape to specify the canonical parameters of the distribution, or
surv, t and shape for the proportion surviving (no events) at time t and shape, or
fail and t and shape for the proportion failing (events) at time t and shape.
scale = -log(surv)·shape/(exp(shape·t))
scale = -log(1-fail)·shape/(exp(shape·t))
The parameters should be spelled correctly as partial matching is not available
Negative shape
A negative shape produces a decreasing hazard whose cumulative hazard is bounded
above by scale / abs(shape) (following Bender, Augustin & Blettner 2005). This
makes the distribution improper: a cure fraction of exp(-scale / abs(shape))
of the subjects never experience the event, so their simulated survival time
(rsurv, rsurvhr, rsurvaft, rsurveh) and invCum_Hfx() are returned as Inf.
Examples
s_gompertz(scale = 1, shape = 1.5)
#> SURVIVAL object
#> Distribution: GOMPERTZ
#> scale : 1
#> shape : 1.5
s_gompertz(surv = 0.4, t = 2, shape = 1.5)
#> SURVIVAL object
#> Distribution: GOMPERTZ
#> scale : 0.07201454
#> shape : 1.5
s_gompertz(fail = 0.6, t = 2, shape = 1.5)
#> SURVIVAL object
#> Distribution: GOMPERTZ
#> scale : 0.07201454
#> shape : 1.5