Annuities. Lecture: Weeks 9-11. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 1 / 43



Similar documents
Insurance Benefits. Lecture: Weeks 6-8. Lecture: Weeks 6-8 (STT 455) Insurance Benefits Fall Valdez 1 / 36

Premium Calculation. Lecture: Weeks Lecture: Weeks (STT 455) Premium Calculation Fall Valdez 1 / 31

Premium Calculation. Lecture: Weeks Lecture: Weeks (Math 3630) Annuities Fall Valdez 1 / 32

Premium Calculation - continued

4. Life Insurance. 4.1 Survival Distribution And Life Tables. Introduction. X, Age-at-death. T (x), time-until-death

How To Perform The Mathematician'S Test On The Mathematically Based Test

1. Datsenka Dog Insurance Company has developed the following mortality table for dogs:

November 2012 Course MLC Examination, Problem No. 1 For two lives, (80) and (90), with independent future lifetimes, you are given: k p 80+k

Manual for SOA Exam MLC.

ACTS 4301 FORMULA SUMMARY Lesson 1: Probability Review. Name f(x) F (x) E[X] Var(X) Name f(x) E[X] Var(X) p x (1 p) m x mp mp(1 p)

May 2012 Course MLC Examination, Problem No. 1 For a 2-year select and ultimate mortality model, you are given:

Manual for SOA Exam MLC.

Solution. Let us write s for the policy year. Then the mortality rate during year s is q 30+s 1. q 30+s 1

MATH 3630 Actuarial Mathematics I Class Test 2 Wednesday, 17 November 2010 Time Allowed: 1 hour Total Marks: 100 points

Chapter You are given: 1 t. Calculate: f. Pr[ T0

Manual for SOA Exam MLC.

Manual for SOA Exam MLC.

Math 630 Problem Set 2

SOCIETY OF ACTUARIES. EXAM MLC Models for Life Contingencies EXAM MLC SAMPLE QUESTIONS

SOA EXAM MLC & CAS EXAM 3L STUDY SUPPLEMENT

Manual for SOA Exam MLC.

1 Cash-flows, discounting, interest rate models

Manual for SOA Exam MLC.

Manual for SOA Exam MLC.

TABLE OF CONTENTS. 4. Daniel Markov 1 173

2. Annuities. 1. Basic Annuities 1.1 Introduction. Annuity: A series of payments made at equal intervals of time.

Mathematics of Life Contingencies MATH 3281

Manual for SOA Exam MLC.

ACTUARIAL MATHEMATICS FOR LIFE CONTINGENT RISKS

Manual for SOA Exam MLC.

SOCIETY OF ACTUARIES. EXAM MLC Models for Life Contingencies EXAM MLC SAMPLE QUESTIONS

Manual for SOA Exam MLC.

JANUARY 2016 EXAMINATIONS. Life Insurance I

Math 419B Actuarial Mathematics II Winter 2013 Bouillon 101 M. W. F. 11:00 11:50

Practice Exam 1. x l x d x

Manual for SOA Exam MLC.

Actuarial Science with

Some Observations on Variance and Risk

Chapter 04 - More General Annuities

1. Revision 2. Revision pv 3. - note that there are other equivalent formulae! 1 pv A x A 1 x:n A 1

Premium calculation. summer semester 2013/2014. Technical University of Ostrava Faculty of Economics department of Finance

Actuarial mathematics 2

INSTITUTE AND FACULTY OF ACTUARIES EXAMINATION

Actuarial Mathematics and Life-Table Statistics. Eric V. Slud Mathematics Department University of Maryland, College Park

Lecture Notes on Actuarial Mathematics

Further Topics in Actuarial Mathematics: Premium Reserves. Matthew Mikola

TABLE OF CONTENTS. GENERAL AND HISTORICAL PREFACE iii SIXTH EDITION PREFACE v PART ONE: REVIEW AND BACKGROUND MATERIAL

Manual for SOA Exam MLC.

Heriot-Watt University. BSc in Actuarial Mathematics and Statistics. Life Insurance Mathematics I. Extra Problems: Multiple Choice

**BEGINNING OF EXAMINATION**

EDUCATION COMMITTEE OF THE SOCIETY OF ACTUARIES MLC STUDY NOTE SUPPLEMENTARY NOTES FOR ACTUARIAL MATHEMATICS FOR LIFE CONTINGENT RISKS VERSION 2.

Lecture Notes on the Mathematics of Finance

Annuities, Insurance and Life

SOCIETY OF ACTUARIES. EXAM MLC Models for Life Contingencies EXAM MLC SAMPLE WRITTEN-ANSWER QUESTIONS AND SOLUTIONS

O MIA-009 (F2F) : GENERAL INSURANCE, LIFE AND

Chapter 03 - Basic Annuities

EXAMINATION. 6 April 2005 (pm) Subject CT5 Contingencies Core Technical. Time allowed: Three hours INSTRUCTIONS TO THE CANDIDATE

TRANSACTIONS OF SOCIETY OF ACTUARIES 1952 VOL. 4 NO. 10 COMPLETE ANNUITIES. EUGENE A. RASOR* Ann T. N. E. GREVILLE

INSTRUCTIONS TO CANDIDATES

Manual for SOA Exam MLC.

2 Policy Values and Reserves

Manual for SOA Exam MLC.

Level Annuities with Payments More Frequent than Each Interest Period

INSTITUTE OF ACTUARIES OF INDIA

n(n + 1) n = 1 r (iii) infinite geometric series: if r < 1 then 1 + 2r + 3r 2 1 e x = 1 + x + x2 3! + for x < 1 ln(1 + x) = x x2 2 + x3 3

Annuities Certain. 1 Introduction. 2 Annuities-immediate. 3 Annuities-due

Financial Mathematics for Actuaries. Chapter 2 Annuities

Financial Mathematics for Actuaries. Chapter 5 LoansandCostsofBorrowing

Annuity is defined as a sequence of n periodical payments, where n can be either finite or infinite.

SOCIETY OF ACTUARIES EXAM M ACTUARIAL MODELS EXAM M SAMPLE QUESTIONS

ACTUARIAL NOTATION. i k 1 i k. , (ii) i k 1 d k

1. Introduction. 1.1 Objective

**BEGINNING OF EXAMINATION**

(Common) Shock models in Exam MLC

6 Insurances on Joint Lives

MATHEMATICS OF FINANCE AND INVESTMENT

SOCIETY OF ACTUARIES EXAM M ACTUARIAL MODELS EXAM M SAMPLE QUESTIONS

More on annuities with payments in arithmetic progression and yield rates for annuities

Actuarial Mathematics for Life Contingent Risks


The Actuary s Free Study Guide for. Second Edition G. Stolyarov II,

Universal Life Insurance

Mathematics of Life Contingencies. Math W Instructor: Edward Furman Homework 1

Let P denote the payment amount. Then the accumulated value of the annuity on the daughter s eighteenth birthday is. P s 18.

Multi-state transition models with actuarial applications c

Nominal rates of interest and discount

Deferred Annuities Certain

EXAMINATIONS. 18 April 2000 (am) Subject 105 Actuarial Mathematics 1. Time allowed: Three hours INSTRUCTIONS TO THE CANDIDATE

Poisson processes (and mixture distributions)

Yanyun Zhu. Actuarial Model: Life Insurance & Annuity. Series in Actuarial Science. Volume I. ir* International Press.

A(t) is the amount function. a(t) is the accumulation function. a(t) = A(t) k at time s ka(t) A(s)

Aggregate Loss Models

INSTITUTE AND FACULTY OF ACTUARIES EXAMINATION

Properties of Future Lifetime Distributions and Estimation

Math 370/408, Spring 2008 Prof. A.J. Hildebrand. Actuarial Exam Practice Problem Set 2 Solutions

DISCOUNTED CASH FLOW VALUATION and MULTIPLE CASH FLOWS

Transcription:

Annuities Lecture: Weeks 9-11 Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 1 / 43

What are annuities? What are annuities? An annuity is a series of payments that could vary according to: timing of payment beginning of year (annuity-due) 1 1 1 1 0 1 2 3 with fixed maturity n-year annuity-due 1 1 1 1 time 0 1 2 n-1 n time more frequently than once a year annuity-due payable m-thly 1 m 1 m 1 m 1 m 1 m 1 m 0 1 m 2 m 1 1 1 m 1 2 m 1 m payable continuously continuous annuity 2 time 1 1 1 end of year (annuity-immediate) 1 1 1 0 1 2 3 n-year annuity-immediate 1 1 1 1 time 0 1 2 n-1 n time annuity-immediate payable m-thly 1 m m 1 1 m m 1 m 1 1 m 0 1 m 2 m 1 1 1 m 1 2 m 2 time 0 1 2 3 time varying benefits Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 2 / 43

What are annuities? annuities-certain Review of annuities-certain annuity-due payable annually ä n = n v k 1 = 1 vn d annuity-immediate a n = n k=1 v k = 1 vn i payable m times a year ä (m) n = 1 m mn 1 v k/m = 1 vn d (m) a (m) n = 1 m mn v k = 1 vn i (m) k=1 ā n = continuous annuity n 0 v t dt = 1 vn δ Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 3 / 43

Chapter summary Chapter summary Life annuities series of benefits paid contingent upon survival of a given life single life considered actuarial present values (APV) or expected present values (EPV) actuarial symbols and notation Types of annuities discrete - due or immediate payable more frequently than once a year continuous varying payments Current payment techniques APV formulas Chapter 5 of Dickson, et al. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 4 / 43

Whole life annuity-due Whole life annuity-due Pays a benefit of a unit $1 at the beginning of each year that the annuitant (x) survives. The present value random variable is Y = ä K+1 where K, in short for K x, is the curtate future lifetime of (x). The actuarial present value of a whole life annuity-due is ä x = E[Y ] = E [ ] ä K+1 = ä k+1 Pr[K = k] = ä k+1 k qx = ä k+1 k p x q x+k Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 5 / 43

Whole life annuity-due current payment technique Current payment technique By writing the PV random variable as Y = I(T > 0) + vi(t > 1) + v 2 I(T > 2) + = one can immediately deduce that [ ] ä x = E[Y ] = E v k I(T > k) = = v k E[I(T > k)] = A straightforward proof of v k p k x = k v k I(T > k), v k Pr[I(T > k)] Ex = A 1 x: k. ä k+1 k qx = v k k p x is in Exercise 5.1. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 6 / 43

Whole life annuity-due - continued Current payment technique - continued The commonly used formula ä x = payment technique for evaluating life annuities. v k p k x is the so-called current Indeed, this formula gives us another intuitive interpretation of what life annuities are: they are nothing but sums of pure endowments (you get a benefit each time you survive). The primary difference lies in when you view the payments: one gives the series of payments made upon death, the other gives the payment made each time you survive. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 7 / 43

Whole life annuity-due some useful formulas Some useful formulas By recalling that ä K+1 = 1 vk+1, we can use this to derive: d relationship to whole life insurance [ ] 1 v K+1 ä x = E = 1 d d (1 A x). Alternatively, we write: A x = 1 dä x. very important formula! the variance formula Var[Y ] = Var [ ] 1 ä K+1 = d 2 Var [ v K+1] = 1 [ 2 d 2 A x (A x ) 2]. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 8 / 43

Whole life annuity-due illustrative example Illustrative example 1 Suppose you are interested in valuing a whole life annuity-due issued to (95). You are given: i = 5%, and the following extract from a life table: x 95 96 97 98 99 100 l x 100 70 40 20 4 0 1 Express the present value random variable for a whole life annuity-due to (95). 2 Calculate the expected value of this random variable. 3 Calculate the variance of this random variable. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 9 / 43

Other types temporary life annuity-due Temporary life annuity-due Pays a benefit of a unit $1 at the beginning of each year so long as the annuitant (x) survives, for up to a total of n years, or n payments. The present value random variable is {ä Y = K+1, K < n ä n, K n = ä. min(k+1,n) The APV of an n-year life annuity-due can be expressed as ä x: n = E[Y ] = = n 1 ä k+1 p k x q x+k + ä n p n x using the current payment technique n 1 v k k p x. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 10 / 43

Other types some useful formulas Some useful formulas Notice that Z = v min(k+1,n) is the PV random variable associated with an n-year endowment insurance, with death benefit payable at EOY. Similar to the case of the whole life, we can use this to derive: relationship to whole life insurance [ ] 1 Z ä x: n = E = 1 ( ) 1 Ax: d d n. Alternatively, we write: A x: n = 1 dä x: n. very important formula! the variance formula Var[Y ] = 1 d 2 Var[Z] = 1 [ 2 d 2 A x: n ( ) ] 2 A x: n. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 11 / 43

Other types deferred whole life annuity-due Deferred whole life annuity-due Pays a benefit of a unit $1 at the beginning of each year while the annuitant (x) survives from x + n onward. The PV random variable can be expressed in a number of ways: Y = { 0, 0 K < n ä = n K+1 n vn ä K+1 n = ä K+1 ä n, K n. The APV of an n-year deferred whole life annuity can be expressed as n äx = E[Y ] = k=n v k p k x = E n x ä x+n = ä x ä x: n. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 12 / 43

Other types variance formula Variance of a deferred whole life annuity-due To derive the variance is not straightforward. The best strategy is to work with and use Y = { 0, 0 K < n v n ä K+1 n, K n Var[Y ] = E[Y 2 ] (E[Y ]) 2 = ) 2 ( v 2n ä k+1 n k qx k=n ä n x Apply a change of variable of summation to say k = k n and then the variance of a whole life insurance issued to (x + n). The variance of Y finally can be expressed as Var[Y ] = 2 d v2n n p x (äx+n ä 2 x+n ) 2 ) ( 2 + 2 n ä x n äx). Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 13 / 43

Other types illustrative example Illustrative example 2 Suppose you are interested in valuing a 2-year deferred whole life annuity-due issued to (95). You are given: i = 6% and the following extract from a life table: x 95 96 97 98 99 100 l x 1000 750 400 225 75 0 1 Express the present value random variable for this annuity. 2 Calculate the expected value of this random variable. 3 Calculate the variance of this random variable. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 14 / 43

Other types recursive relationships Recursive relationships The following relationships are easy to show: ä x = 1 + vp x ä x+1 = 1 + 1 E x ä x+1 = 1 + vp x + v 2 2 p x ä x+2 = 1 + 1 E x + 2 E x ä x+2 In general, because E s are multiplicative, we can generalized this recursions to n 1 ä x = kex = kex + kex k=n apply change of variable k = k n = ä x: n + nex k Ex+n = ä x: n + n E k =0 = ä x: n + n E x ä x+n = ä x: n + ä n x x k k =0 E x+n The last term shows that a whole life annuity is the sum of a term life annuity and a deferred life annuity. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 15 / 43

Other types parameter sensitivity äx 10 20 30 40 50 i = 1% i = 5% i = 10% i = 15% i = 20% äx 5 10 15 20 c = 1.124 c = 1.130 c = 1.136 c = 1.142 c = 1.148 20 40 60 80 100 x 20 40 60 80 100 x Figure : Comparing APV of a whole life annuity-due for based on the Standard Ultimate Survival Model (Makeham with A = 0.00022, B = 2.7 10 6, c = 1.124). Left figure: varying i. Right figure: varying c with i = 5% Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 16 / 43

Life annuity-immediate whole life Whole life annuity-immediate Procedures and principles for annuity-due can be adapted for annuity-immediate. Consider the whole life annuity-immediate, the PV random variable is clearly Y = a K so that APV is given by a x = E[Y ] = Relationship to life insurance: Y = 1 i ( 1 v K ) = 1 i leads to 1 = ia x + (1 + i)a x. a K p k x q x+k = k=1 v k p k x. [ 1 (1 + i)v K+1 ] Interpretation of this equation - to be discussed in class. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 17 / 43

Life annuity-immediate other types Other types of life annuity-immediate For an n-year life annuity-immediate: Find expression for the present value random variable. Express formulas for its actuarial present value or expectation. Find expression for the variance of the present value random variable. For an n-year deferred whole life annuity-immediate: Find expression for the present value random variable. Give expressions for the actuarial present value. Details to be discussed in lecture. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 18 / 43

Life annuities with m-thly payments Life annuities with m-thly payments In practice, life annuities are often payable more frequently than once a year, e.g. monthly (m = 12), quarterly (m = 4), or semi-annually (m = 2). Here, we define the random variable K x (m), or simply K (m), to be the complete future lifetime rounded down to the nearest 1/m-th of a year. For example, if the observed T = 45.86 for a life (x) and m = 4, then the observed K (4) is 45 3 4. Indeed, we can write K (m) = 1 m mt, where is greatest integer (or floor) function. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 19 / 43

Life annuities with m-thly payments whole life annuity-due Whole life annuity-due payable m times a year Consider a whole life annuity-due with payments made m times a year. Its PV random variable can be expressed as Y = ä (m) K (m) +(1/m) = 1 vk(m)+(1/m) d (m). The APV of this annuity is Variance is E[Y ] = ä (m) x Var[Y ] = = 1 m v h/m h/mpx = 1 A(m) x d (m). h=0 [ ] Var v K(m) +(1/m) ( ) d (m) 2 = 2 (m) Ax ( ) A (m) 2 x ( ) d (m) 2. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 20 / 43

Life annuities with m-thly payments some useful relationships Some useful relationships Here we list some important relationships regarding the life annuity-due with m-thly payments (Note - these are exact formulas): 1 = dä x + A x = d (m) ä (m) x + A (m) x ä (m) x = d d (m) äx 1 d (m) ( A (m) x A x ) = ä (m) 1 ä x ä (m) ( A (m) x A x ) ä (m) x = 1 A(m) x d (m) = ä (m) ä(m) A(m) x Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 21 / 43

Life annuities with m-thly payments other types Other types of life annuity-due payable m-thly n-year term PV random variable Y = ä (m) APV symbol E[Y ] = ä (m) x: n current payment technique other relationships = 1 m = ä (m) x min(k (m) +(1/m),n) mn 1 h=0 relation to life insurance = 1 d (m) [ n-year deferred PV random variable Y = v n ä (m) APV symbol E[Y ] = ä (m) n x current payment technique = 1 m v h/m n E x ä (m) x+n ] 1 A (m) x: n K (m) +(1/m) n h=mn other relationships = n E x ä (m) relation to life insurance = 1 [ d (m) E v h/m x+n = ä(m) x p h/m x I(K n) p h/m x n x A (m) n x ä (m) x: n ] Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 22 / 43

Life annuities with m-thly payments illustrative example Illustrative example 3 Professor Balducci is currently age 60 and will retire immediately. He purchased a whole life annuity-due contract which will pay him on a monthly basis the following benefits: $12,000 each year for the next 10 years; $24,000 each year for the following 5 years after that; and finally, $48,000 each year thereafter. You are given: i = 3% and the following table: x 1000A (12) x p 5 x 60 661.11 0.8504 65 712.33 0.7926 70 760.65 0.7164 75 804.93 0.6196 Calculate the APV of Professor Balducci s life annuity benefits. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 23 / 43

Continuous whole life annuity (Continuous) whole life annuity A life annuity payable continuously at the rate of one unit per year. One can think of it as life annuity payable m-thly per year, with m. The PV random variable is Y = ā T (x). where T is the future lifetime of The APV of the annuity: ā x = E[Y ] = E [ ā T ] = = 0 ā t p t x µ x+t dt use integration by parts - see page 117 for proof 0 v t p t x dt = 0 texdt Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 24 / 43

Continuous whole life annuity - continued One can also write expressions for the cdf and pdf of Y in terms of the cdf and pdf of T. For example, Pr[Y y] = Pr [ 1 v T δy ] [ ] log(1 δy) = Pr T log v Recursive relation: ā x = ā x: 1 + vp x ā x+1 Variance expression: Var [ [ ] ] 1 v T ā T = Var Relationship to whole life insurance: Ā x = 1 δā x δ = 1 [ 2 Ā δ 2 x ( ) ] 2 Ā x Try writing explicit expressions for the APV and variance where we have constant force of mortality and constant force of interest. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 25 / 43

Continuous temporary life annuity Temporary life annuity A (continuous) n-year temporary life annuity pays 1 per year continuously while (x) survives during the next n years. {ā The PV random variable is Y = T, 0 T < n = ā ā n, T n min(t,n) The APV of the annuity: ā x: n = E[Y ] = + n n 0 ā t t p x µ x+t dt ā n p t x µ x+t dt = Recursive formula: ā x: n = ā x: 1 + vp x ā x+1: n 1. n 0 v t p t x dt. To derive variance, one way to get explicit form is to note that Y = (1 Z) /δ where Z is the PV r.v. for an n-year endowment ins. [details in class.] Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 26 / 43

Continuous deferred whole life annuity Deferred whole life annuity Pays a benefit of a unit $1 each year continuously while the annuitant (x) survives from x + n onward. The PV random variable is { 0, 0 T < n Y = v n ā T n, T n { 0, 0 T < n =. ā T ā n, T n The APV [expected value of Y ] of the annuity is n āx = n E x ā x = ā x ā x: n = The variance of Y is given by Var[Y ] = 2 δ v2n n p x (āx+n ā 2 x+n n ) ( v t p t x dt. ) 2 n āx Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 27 / 43

Continuous special mortality laws Special mortality laws Just as in the case of life insurance valuation, we can derive nice explicit forms for life annuity formulas in the case where mortality follows: constant force (or Exponential distribution); or De Moivre s law (or Uniform distribution). Try deriving some of these formulas. You can approach them in a couple of ways: Know the results for the life insurance case, and then use the relationships between annuities and insurances. You can always derive it from first principles, usually working with the current payment technique. In the continuous case, one can use numerical approximations to evaluate the integral: trapezium (trapezoidal) rule repeated Simpson s rule Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 28 / 43

Other forms varying benefits Life annuities with varying benefits Some of these are discussed in details in Section 5.10. You may try to remember the special symbols used, especially if the variation is a fixed unit of $1 (either increasing or decreasing). The most important thing to remember is to apply similar concept of discounting with life taught in the life insurance case (note: this works only for valuing actuarial present values): work with drawing the benefit payments as a function of time; and use then your intuition to derive the desired results. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 29 / 43

Evaluating annuities Methods for evaluating annuity functions Section 5.11 Recursions: For example, in the case of a whole life annuity-due on (x), recall ä x = 1 + vp x ä x+1. Given a set of mortality assumptions, start with ä x = v k k p x and then use the recursion to evaluate values for subsequent ages. UDD: deaths are uniformly distribution between integral ages. Woolhouse s approximations Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 30 / 43

Evaluating annuities UDD Uniform Distribution of Deaths (UDD) Under the UDD assumption, we have derived in the previous chapter that the following holds: A (m) x = i i (m) A x Then use the relationship between annuities and insurance: ä (m) x = 1 A(m) x d (m) This leads us to the following result when UDD holds: where ä (m) x = α (m) ä x β (m), α (m) = s (m) ä (m) = i 1 1 i (m) d d (m) β (m) = s(m) 1 d (m) 1 = i i(m) i (m) d (m) Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 31 / 43

Evaluating annuities Woolhouse s formulas Woolhouse s approximate fomulas The Woolhouse s approximate formulas for evaluating annuities are based on the Euler-Maclaurin formula for numerical integration: 0 g(t)dt = h g(kh) h h2 g(0) + 2 12 g (0) h4 720 g (0) + for some positive constant h. This formula is then applied to g(t) = v t p t x which leads us to g (t) = v t p t x (δ µ x+t ). We can obtain the following Woolhouse s approximate formula: ä (m) x ä x m 1 2m m2 1 12m 2 (δ + µ x) Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 32 / 43

Evaluating annuities Woolhouse s formulas Approximating an n-year temporary life annuity-due with m-thly payments Apply the Woolhouse s approximate formula to ä (m) x: n = ä(m) x n E x ä (m) x+n This leads us to the following Woolhouse s approximate formulas: Use 2 terms (W2) Use 3 terms (W3) ä (m) x: n ä x: n m 1 2m (1 n E x) ä (m) x: n ä x: n m 1 2m (1 n E x) Use 3 terms (W3*) m2 1 [δ + µ 12m 2 x n E x (δ + µ x+n )] use approximation for force of mortality (modified) µ x 1 2 [log(p x 1) + log(p x )] Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 33 / 43

Woolhouse s formulas numerical illustrations Numerical illustrations We compare the various approximations: UDD, W2, W3, W3* based on the Standard Ultimate Survival Model with Makeham s law µ x = A + Bc x, where A = 0.00022, B = 2.7 10 6 and c = 1.124. The results for comparing the values for: ä (12) x: 10 ä (2) x: 25 with i = 10% with i = 5% are summarized in the following slides. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 34 / 43

Woolhouse s formulas numerical illustrations Values of ä (12) x: 10 with i = 10% x ä x ä (12) x 10Ex Exact UDD W2 W3 W3* 20 10.9315 10.4653 0.384492 6.4655 6.4655 6.4704 6.4655 6.4655 30 10.8690 10.4027 0.384039 6.4630 6.4630 6.4679 6.4630 6.4630 40 10.7249 10.2586 0.382586 6.4550 6.4550 6.4599 6.4550 6.4550 50 10.4081 9.9418 0.377947 6.4295 6.4294 6.4344 6.4295 6.4295 60 9.7594 9.2929 0.363394 6.3485 6.3482 6.3535 6.3485 6.3485 70 8.5697 8.1027 0.320250 6.0991 6.0982 6.1044 6.0990 6.0990 80 6.7253 6.2565 0.213219 5.4003 5.3989 5.4073 5.4003 5.4003 90 4.4901 4.0155 0.057574 3.8975 3.8997 3.9117 3.8975 3.8975 100 2.5433 2.0505 0.000851 2.0497 2.0699 2.0842 2.0497 2.0496 Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 35 / 43

Woolhouse s formulas numerical illustrations Values of ä (2) x: 25 with i = 5% x ä x ä (2) x 25Ex Exact UDD W2 W3 W3* 20 19.9664 19.7133 0.292450 14.5770 14.5770 14.5792 14.5770 14.5770 30 19.3834 19.1303 0.289733 14.5506 14.5505 14.5527 14.5506 14.5506 40 18.4578 18.2047 0.281157 14.4663 14.4662 14.4684 14.4663 14.4663 50 17.0245 16.7714 0.255242 14.2028 14.2024 14.2048 14.2028 14.2028 60 14.9041 14.6508 0.186974 13.4275 13.4265 13.4295 13.4275 13.4275 70 12.0083 11.7546 0.068663 11.5117 11.5104 11.5144 11.5117 11.5117 80 8.5484 8.2934 0.002732 8.2889 8.2889 8.2938 8.2889 8.2889 90 5.1835 4.9242 0.000000 4.9242 4.9281 4.9335 4.9242 4.9242 100 2.7156 2.4425 0.000000 2.4425 2.4599 2.4656 2.4424 2.4424 Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 36 / 43

Woolhouse s formulas visualizing the differences Figure : Visualizing the different approximations for ä (2) x: 25 Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 37 / 43 Exact minus UDD -0.020-0.010 0.000 Exact minus W2-0.025-0.015-0.005 20 27 34 41 48 55 62 69 76 83 90 97 age x 20 27 34 41 48 55 62 69 76 83 90 97 age x Exact minus W3-0.002-0.001 0.000 0.001 0.002 Exact minus W3* -0.002-0.001 0.000 0.001 0.002 20 27 34 41 48 55 62 69 76 83 90 97 20 27 34 41 48 55 62 69 76 83 90 97 age x age x

Woolhouse s formulas illustrative example Illustrative example 4 You are given: i = 5% and the following table: Approximate ä (12) 50: 3 1 UDD assumptions x l x µ x 49 811 0.0213 50 793 0.0235 51 773 0.0258 52 753 0.0284 53 731 0.0312 54 707 0.0344 based on the following methods: 2 Woolhouse s formula using the first two terms only 3 Woolhouse s formula using all three terms 4 Woolhouse s formula using all three terms but approximating the force of mortality Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 38 / 43

Additional practice problems Practice problem 1 You are given: l x = 115 x, for 0 x 115 δ = 4% Calculate ä 65: 20. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 39 / 43

Additional practice problems Practice problem 2 You are given: µ x+t = 0.03, for t 0 δ = 5% Y is the present value random variable for a continuous whole life annuity of $1 issued to (x). [ Calculate Pr Y E[Y ] ] Var[Y ]. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 40 / 43

Additional practice problems Practice problem 3 - modified SOA MLC Spring 2012 For a whole life annuity-due of $1,000 per year on (65), you are given: Mortality follows Gompertz law with µ x = Bc x, for x 0, where B = 5 10 5 and c = 1.1. i = 4% Y is the present value random variable for this annuity. Calculate the probability that Y is less than $11,500. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 41 / 43

Additional practice problems Practice problem 4 - SOA MLC Spring 2014 For a group of 100 lives age x with independent future lifetimes, you are given: Each life is to be paid $1 at the beginning of each year, if alive. A x = 0.45 2A x = 0.22 i = 0.05 Y is the present value random variable of the aggregate payments. Using the Normal approximation to Y, calculate the initial size of the fund needed in order to be 95% certain of being able to make the payments for these life annuities. Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 42 / 43

Other terminologies Other terminologies and notations used Expression temporary life annuity-due annuity-immediate Other terms/symbols used term annuity-due n-year term life annuity-due immediate annuity annuity immediate Lecture: Weeks 9-11 (STT 455) Annuities Fall 2014 - Valdez 43 / 43