Simulation of Risk Processes

We conduct empirical studies for Danish fire losses recorded by Copenhagen Re. The data concerns major Danish fire losses in Danish Krone (DKK), occurred between 1980 and 2002 and adjusted for inflation. Only losses of profits connected with the fires are taken into consideration. We start the analysis with a HPP with a constant intensity λ1. Studies of the quarterly numbers of losses and the inter-occurrence times of the fires lead us to the conclusion that the annual intensity ofλ1 = 98.39 gives the best fitted HPP.

However, as we can see in the right panel of Figure 1.9, the fit is not very good suggesting that the HPP is too simplistic. A renewal process would also give unsatisfactory results as the data reveals a clear increasing trend in the number of quarterly losses, see the left panel in Figure 1.9. This leaves us with the NHPP. We tested different exponential and polynomial functional forms, but a simple linear intensity function λ2(s) = c+ds gives the best fit. Applying the least squares procedure we arrive at the following values of the parameters: c = 17.99 and d = 7.15. Processes with both choices of the intensity function,λ1andλ2(s), are illustrated in the right panel of Figure 1.9, where the accumulated number of fire losses and mean value functions for all 23 years of data are depicted.

1.5 Applications 33

Figure 1.10: The Danish fire data simulation results for a NHPP with log-normal claim sizes (left panel) and a NHPP with Burr claim sizes (right panel). The dotted lines are the sample 0.001, 0.01, 0.05, 0.25, 0.50, 0.75, 0.95, 0.99, 0.999-quantile lines based on 3000 tra-jectories of the risk process.

STF2loss10.m

After describing the claim arrival process we have to find an appropriate model for the loss amounts. In Section 1.5.1 a number of distributions were fitted to loss sizes. The log-normal distribution with parametersµ = 12.525 and σ= 1.5384 produced the best results. The Burr distribution withα= 0.9844, λ = 1.0585·10⁶, and τ = 1.1096 overestimated the tails of the empirical distribution, nevertheless it gave the next best fit.

The simulation results are presented in Figure 1.10. We consider a hypothetical scenario where the insurance company insures losses resulting from fire damage.

The company’s initial capital is assumed to beu= 400 million DKK and the relative safety loading used is θ = 0.5. We choose two models of the risk process whose application is most justified by the statistical results described above: a NHPP with log-normal claim sizes and a NHPP with Burr claim sizes. In both panels the thick solid blue line is the “real” risk process, i.e.

a trajectory constructed from the historical arrival times and values of the losses. The different shapes of the “real” risk process in the two panels are due to the different forms of the premium functionc(t) which has to be chosen accordingly to the type of the claim arrival process. The dashed red line is a sample trajectory. The thin solid lines are the sample 0.001, 0.01, 0.05, 0.25,

0.50, 0.75, 0.95, 0.99, 0.999-quantile lines based on 3000 trajectories of the risk process. We assume that if the capital of the insurance company drops bellow zero, the company goes bankrupt, so the capital is set to zero and remains at this level hereafter.

Comparing the log-normal and Burr claim size models, we can conclude that in the latter model extreme events are more likely to happen. This is manifested by wider quantile lines in the right panel of Figure 1.10. Since for log-normal claim sizes the historical trajectory is above the 0.01-quantile line for most of the time, and taking into account that we have followed a non-robust estimation approach of loss severities, we suggest to use this specification for further risk process modeling using the 1980-2002 Danish fire losses dataset.

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