ACTL30001 Actuarial Modelling I — 2023
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ACTL30001 Actuarial Modelling I — 2023
COVER SHEET
Assignment 1
Due at 5:00PM on Friday, April 7, 2023
1. (25 marks) Suppose force of mortality is given by µy = a + by + cy2 for all 0 < y < 120 where a, b, and c are constants and c > 0. You are also given that no one can survive to age 120.
(a) Calculate and simplify the expression for tpx .
(b) What constraints should be imposed on the values of a, b, and c?
(c) You are given a = 0.002, b=−0.000254.
i. Find the value of c such that e0 = 59.5 using goal seeker in Excel. Describe the steps you took to find the value.
ii. Does there exist a value of c such that e0 = 80 and why?
(d) Let l0 = 100, 000. Using the approximation e(◦)x ⇡ ex + 0.5 and Excel to construct a mortality table based on this mortality law using the values of a and b specified in 1c and the value of c determined in 1(c)i.
The constructed mortality table should have columns with heading lx , x = 0, 1, 2, . . . , 120,
dx ,px ,qx ,µx ,e(◦)x , Tx ,Lx , x = 0, 1, 2, . . . , 119.
Round lx ,Lx and Tx to the nearest integer. Describe how you obtain Tx and Lx .
(e) Comment on whether the constructed mortality table is suitable for human mortality.
(f) Based on your constructed Life Table in 1d,
i. compute f50 (1.5) to 4 significant digits, if the uniform distribution of deaths (UDD) assumption applies, where fx (t) is the density of Tx at time t;
ii. compute 0.5|1.5 q50.5 to 4 significant digits, if CFM assumption ap- plies;
2. (25 marks) Suppose µy = m1 for all y < 30 and µy = m2 for all y > 30. (m1 < m2 are constants).
(a) Determine the distribution function of Tx , the future lifetime of (x). (b) Calculate and simplify the expression for e(◦)x and ex .
(c) Let m1 = 0.03 and m2 = 0.04. Compute 10p25 ,e(◦)25 and e25 .
(d) Let Kx = [Tx]. Find the probability mass function of Kx .
(e) Define y = P(K0 = y|K0 ≥ y) to be the hazard function of K0 at y for y = 0, 1, 2, . . . . Find y .
3. (5 marks) You are told that for a fixed x0 > 0 and all t ≥ 0, tpx0 = atb e −ct2 −dt, where a,b,c,d are constants. Find all the restrictions on a,b,c,d.
(For instance, a > 2,b < 0, etc.)
4. (5 marks) Which of the following functions could be the hazard rate µx of some positive random variable (not necessarily representing human lifetime), for all x larger than some x0 ≥ 0? Justify your answers.
(a) , if C is a positive constant.
(b) , if C1 ,C2 are positive constants.
(c) C1 eC2北, if C1 ,C2 are positive constants.
5. (15 marks) You are given l102 = 10, l103 = 5.
(a) Plot the three curves {1−tq10(U)2+t , 1−tq10(B)2+t , 1−tq10(C)2+t} for 0 < t < 1 on the same graph, if U refers to UDD, B refers to the Balducci assump- tion, and C refers to the constant force of mortality assumption.
(b) Compute the maximum of the di↵erence |1−tq10(U)2+t − 1−tq10(B)2+t| for 0 < t < 1.
6. (15 marks) Eight lives aged 40 under observation gave the following data:
deaths times: 3.2, 4.5, 6.8, 9.3
withdrawal times: 1.2, 4.5, 5.5, 8.0
(a) Compute the K-M estimate of S(t), for all t;
(b) Plot the K-M estimate of S(t).
(c) Assume that the future lifetime of (x)follows the distribution F北 (t;✓) = 1 − e−✓t , ✓ > 0.
i. Write down the likelihood function from the data above.
ii. Find the MLE of ✓ .
2023-04-07