Sample Questions
If , then the mean of is:
With and :
Tail classification by hazard rate behavior:
- Increasing hazard rate (IHR): lighter than exponential, with a tail that decays faster than for some .
- Constant hazard rate: the exponential distribution, light-tailed, with MGF defined for .
- Decreasing hazard rate (DHR): heavier than exponential, with a survival function that decays slower than any pure exponential.
The exponential sits at the boundary between IHR (lighter) and DHR (heavier) distributions. It is classified as light-tailed because its MGF exists on a non-trivial interval containing a neighborhood of zero, namely .
For the lognormal with parameters and , define . The mean excess loss at is: , where . With , , : . . , . . .