Table 1.

Survival distributions

Distribution	Probability density function f(t)	Survival function S(t)*	Parameters	With covariates
Exponential	λe−λt	e−λt	λ = rate
Gamma			λ = rate v = shape
Weibull			λ = rate v = shape
Log-normal			μ = mean τ = precision

^*Φ is the standard normal cumulative distribution function, and γ is the lower incomplete gamma function.