define_survival: Define a survival process

In simulab: Simulates a Wide Variety of Data Shapes, Sizes and Distributions

Define a survival process

Description

Records one Weibull hazard segment for one event time. The simstudy parameterization is used throughout: an event time drawn from this segment has survival function S(t) = exp(-exp(formula) * t^(1 / shape) / scale), so shape is the reciprocal of the textbook Weibull shape, and exp(formula) multiplies the whole cumulative hazard. A coefficient inside formula is therefore a log hazard ratio, while formula itself equals the log hazard only when shape and scale are both 1.

Usage

define_survival(event, formula = 0, scale = 1, shape = 1, transition = 0)

Arguments

event	Name of the event-time variable. A single non-empty string.
formula	Linear predictor on the log scale, given as a number, a string, or an unquoted expression over the covariate columns (for example "-8 + 0.5 * treatment"). Defaults to 0. It is stored as text and evaluated row by row against the data.
scale	Positive Weibull scale, as a number, a string, or an expression over the covariates. Defaults to 1. It divides the cumulative hazard.
shape	Positive Weibull shape in the simstudy parameterization (the exponent applied to the transformed time, so the hazard is constant when shape is 1 and decreasing when shape is above 1). Defaults to 1.
transition	Time at which this hazard segment begins. A single finite non-negative number, defaulting to 0. The first segment of an event must start at 0.

Value

A one-row simulab_survival_spec base data.frame with columns event, formula, scale and shape (all character, the stored definition text) and the numeric column transition.

Examples

define_survival("time", formula = -8, shape = 0.3)

simulab documentation built on Oct. 15, 2026, 5:08 p.m.