Loss Models: From Data to Decisions, 4th Edition
by Stuart A. Klugman, Harry H. Panjer, Gordon E. Willmot
14.5 Compound models
For the method of moments, the first few moments can be matched with the sample moments. The system of equations can be solved to obtain the moment-based estimators. Note that the number of parameters in the compound model is the sum of the number of parameters in the primary and secondary distributions. The first two theoretical moments for compound distributions are
![]()
These results are developed in Chapter 9. The first three moments for the compound Poisson distribution are given in (7.10).
Maximum likelihood estimation is also carried out as before. The loglikelihood to be maximized is
![]()
When gk is the probability of a compound distribution, the loglikelihood can be maximized numerically. The first and second derivatives of the loglikelihood can be obtained by using approximate differentiation methods as applied directly to the loglikelihood function at the maximum value.
EXAMPLE 14.8
Determine various properties of the Poisson–zero-truncated geometric distribution. This distribution is also called the Polya–Aeppli distribution.
For the zero-truncated geometric distribution, the pgf is
and therefore the pgf of the Polya–Aeppli distribution is
The mean is
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access