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Actuarial Modelling of Claim Counts Risk Classification, Credibility ...

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178 <strong>Actuarial</strong> <strong>Modelling</strong> <strong>of</strong> <strong>Claim</strong> <strong>Counts</strong><br />

The convergence is now much slower:<br />

⎛<br />

P 5 01 =<br />

⎜<br />

⎝<br />

0791523 0081985 0088694 0018169 0015456 0004173<br />

0788490 0066822 0106890 0017259 0014546 0005992<br />

0788490 0063789 0073531 0053651 0013637 0006902<br />

0606531 0245749 0070498 0020292 0050028 0006902<br />

0606531 0063789 0252457 0017259 0034865 0025098<br />

0606531 0063789 0070498 0199219 0031833 0028131<br />

⎞<br />

⎟<br />

⎠<br />

⎛<br />

P 10 01 =<br />

⎜<br />

⎝<br />

0784013 0081747 0090966 0022022 0016217 0005037<br />

0784003 0081480 0090248 0023009 0016178 0005081<br />

0777382 0088092 0089871 0022071 0017497 0005087<br />

0776278 0079263 0099795 0021694 0016890 0006080<br />

0776278 0078160 0090966 0031618 0016623 0006356<br />

0743169 0111269 0089862 0026100 0023236 0006365<br />

⎞<br />

⎟<br />

⎠<br />

⎛<br />

P 20 01 =<br />

⎜<br />

⎝<br />

which slowly converges to<br />

⎛<br />

01 =<br />

⎜<br />

⎝<br />

0782907 0082338 0090996 0022276 0016387 0005096<br />

0782903 0082332 0091006 0022275 0016387 0005097<br />

0782902 0082326 0090993 0022295 0016386 0005098<br />

0782803 0082424 0090984 0022285 0016406 0005098<br />

0782776 0082352 0091082 0022278 0016403 0005108<br />

0782774 0082327 0091011 0022376 0016399 0005113<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

0782901 0082338 0090998 0022278 0016387 0005097<br />

In this case, the system is not stable after 20 years.<br />

Let us consider the trajectory <strong>of</strong> a policyholder with expected claim frequency <br />

accross the levels <strong>of</strong> the bonus-malus scale. We define the stationary distribution =<br />

0 1 s T as follows: l is the stationary probability for a policyholder<br />

with mean frequency to be in level l i.e.<br />

l2<br />

= lim<br />

n→+ pn l 1 l 2<br />

<br />

The term l is the limit value <strong>of</strong> the probability that the policyholder is in level l, when<br />

the number <strong>of</strong> periods tends to +. It is also the fraction <strong>of</strong> the time a policyholder with<br />

claim frequency spends in level l, once the steady state has been reached. Note that <br />

⎞<br />

⎟<br />

⎠<br />

⎞<br />

<br />

⎟<br />

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