• We are pleased to announce that the winner of our Feedback Prize Draw for the Winter 2024-25 session and winning £150 of gift vouchers is Zhao Liang Tay. Congratulations to Zhao Liang. If you fancy winning £150 worth of gift vouchers (from a major UK store) for the Summer 2025 exam sitting for just a few minutes of your time throughout the session, please see our website at https://www.acted.co.uk/further-info.html?pat=feedback#feedback-prize for more information on how you can make sure your name is included in the draw at the end of the session.
  • Please be advised that the SP1, SP5 and SP7 X1 deadline is the 14th July and not the 17th June as first stated. Please accept out apologies for any confusion caused.

September 2003 - Question 2

MindFull

Ton up Member
In the past paper solution for this question, it seemed like the examiners used N as a negative binomial distribution, and the probability of an event as a binomial distribution. In order to get the expectation and variance of the total number of claims, I think they used the E[E[T|N]] and the (E[X])^2*V[N] + V[X]E[N]. But it seems that the mean of the neg. binomial distribution was squared instead of the mean of the binomial. Does anyone understand the examiners' answer to this question?

Thanks.
 
In the past paper solution for this question, it seemed like the examiners used N as a negative binomial distribution, and the probability of an event as a binomial distribution. In order to get the expectation and variance of the total number of claims, I think they used the E[E[T|N]] and the (E[X])^2*V[N] + V[X]E[N]. But it seems that the mean of the neg. binomial distribution was squared instead of the mean of the binomial. Does anyone understand the examiners' answer to this question?

Thanks.

It's a type 1 negative binomial (rather than the usual type 2 negative binomial)
 
It's a type 1 negative binomial (rather than the usual type 2 negative binomial)

I figured out that it's a Type 1 Neg. Binomial, but I'm still a bit lost on how the final answer, especially for the variance of the total number of claims was arrived at. For the total number of claims. Do we assume that the distribution of an event occurring is Binomial, with p = .02 and then multiply the variances to get the variance of the total number of claims?

Thanks much.

P.S. I'm also still unsure as to how to interpret the question. The neg. binomial type 2 is the # of failures until the kth success... So how does this definition make the distribution of the number of events given an event occurred distributed by a neg. binomial?

Thanks Mr. Lee
 
I figured out that it's a Type 1 Neg. Binomial, but I'm still a bit lost on how the final answer, especially for the variance of the total number of claims was arrived at. For the total number of claims. Do we assume that the distribution of an event occurring is Binomial, with p = .02 and then multiply the variances to get the variance of the total number of claims?

There are three ways of answering this question.

This is describing an individual risk model - as there is a maximum of one event per risk. So you could just use the standard individual risk model formulae:

E(S) = sum (mq)
var(S) = sum (qs² + q(1-q)m²)

where q= probability of a claim (or in this case an event)
m = mean of each claim, s² = variance of each claim

Secondly, since each event for the risks is identical we could use the collective risk model formulae given on page 16 of the Tables with N~Bin(120,0.02).

Thirdly, we could torture ourselves with the horrendous conditional formulae.

P.S. I'm also still unsure as to how to interpret the question. The neg. binomial type 2 is the # of failures until the kth success... So how does this definition make the distribution of the number of events given an event occurred distributed by a neg. binomial?

It doesn't fit here it's simply used because it starts at 1.
 
Last edited:
There are three ways of answering this question.

This is describing an individual risk model - as there is a maximum of one event per risk. So you could just use the standard individual risk model formulae:

E(S) = sum (mq)
var(S) = sum (qs² + q(1-q)m²)

where q= probability of a claim (or in this case an event)
m = mean of each claim, s² = variance of each claim

Secondly, since each event for the risks is identical we could use the collective risk model formulae given on page 16 of the Tables with N~Bin(120,0.02).

Thirdly, we could torture ourselves we the horrendous conditional formulae.



It doesn't fit here it's simply used because it starts at 1.

Thanks so much Mr. Lee.
 
Back
Top