Model | S(y) | Parameter restrictions | Mean |
---|
Weibull: | exp (-λyγ) | λ > 0, γ > 0 |
|
Gamma: |
| α > 0, β > 0 |
αβ
|
Gompertz: |
| γ > 0 | No closed formula |
Log-Logistic: |
| α > 0, β > 0 |
|
Log-Normal: |
| σ > 0 |
|
- † I(a, x) is the incomplete gamma function given by
- ‡ Φ(x) is the standard normal cdf given by
- For each distribution the survivor function S(y) is given accompanied by parameter restrictions, if applicable, and the formula for the mean survival as a function of parameters.