International Actuarial Notation 123
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INTERNATIONAL ACTUARIAL NOTATION 123 INTERNATIONAL ACTUARIAL NOTATION ВУ F. S. PERRYMAN The Council of the Society announces that the revised International Actuarial N otation, particulars of which are given below, will Ье adopted in the Proceedings of the Society as from the present Number. The re vised Notation will also Ье used Ьу the Examination Committee for all examinations subsequent to those in Мау, i950. The revised Notation has been adopted Ьу the Society of Actuaries and also Ьу the Institute of Actuaries in England, the Faculty of Actuaries in Scotland and Ьу actuarial societies in various other foreign countries. Before giving an account of the circumstances leading up to the present revision and а complete account of the Notation it is desiraЫe to state here the principal changes which are now being introducd: " ( 1) Interest. In place of the symbol j (m) =the nominal rate of interest convertiЫe m times in а year when the effective rate is i, the symbol j(m) has been substituted; the former defini- tions of i (m) and [ as the effective rate of interest when interest is convertiЫe m times а year and momently respec tively have been abolished. "(2) Annuities-due. In place of the symbol а for an annuity under which the first payment is to Ье made at once the symbol а has been adopted. This adoption of the trema " as а symbol of acceleration has permitted the introduction of s for the ac cumulated amount of an annuity-due at the end of the term, for which no symbol previously existed. "(3) Mortality. The use of Q for the probaЬility of dying within а longer term than 1 year has been omitted. " (4) Compound symbols. The use of D in а compound symbol to indicate decreasing benefits has been introduced. "(5) Commutation columns. The old definition of Nx=Dx+i + Dx+ 2 + Dх+з etc. has been abolished in favour of Nx = Dx+ Dx+1 +Dx+2 etc. This renders the use of Nx and Nx for the latter series un necessary." The complete statement of the revised Notation and its history follows: 124 INTERNATIONAL ACTUARIAL NOTATION The existing international actuarial notation was founded on the ' Кеу to the Notatioп' given in the ]nstitute of Actuaries Text-Book, Part 11, Ltfe Con tingencies, Ьу George Кing, and is embodied in an exp\anatory statement adopted unaпimously Ьу the Second International Actuarial Congress held in London in Мау 1898 and printed оп рр. 618-40 of the Transactions of that Coпgress. At the Third lnterпatioпal Congress held iп Paris iri Juпe 1900 а further statemeпt Ьу Dr Sprague was submitted which rearranged the symbols iп different orders and grouped them оп differeпt principles but did поt iпtro duce апу chaпges iп the symbols themselves Ьеуопd two slight additioпs. This statemeпt is printed оп рр. 622-51 of the Transactions of that Congress. At the Eleventh Iпternational Congress held in Paris in Juпe 1937 an Iпternatioпal Committee was appoiпted to coпsider the question of пotation апd giveп the duty of submitting defiпite proposals to the пехt Congress. This Committee met iп Brussels iп July 1938 апd again in July 1939, апd certaiп chaп.,ges would have been propbsed for adoption at Lucerne iп l 940. 0·.ving to the war this could nQt Ье dопе, but in or.der not to lose the benefit of these changes for an indefinite · period the Iпstitute of Actuaries апd the Faculty of Actuaries have decided to adopt at а date to Ье mutually arranged those recommeпdatioпs which had received uпaпimous or substaпtial support at the meetiпgs of the Committee. As тапу studeпts апd members of the professioп have not ready access to the above-mentioned Transactions it has Ьееп thought desiraЬle to prepare апd issue the followiпg statemeпt of the Iпterпational Actuarial Notatioп after embodying iп it the chaпges arisiпg from the recommeпdations mentioned above. The geпeral principles оп which the system is based are as follows: То each fuпdamental symbolic letter are attached signs апd letters each haviпg its оwп sigпification. The lower space to the left is reserved for signs indicatiпg the coпditions relative to the duratioп of the operations and to their position with regard to time. The lower space to the right is r•:served for sigпs iпdicatiпg the conditioпs relative to ages and the order of succession of the everits. The upper space to the right is reserved for sigпs indicatiпg the periodicity of the events. The upper space to the left is free, and in it сап Ье placed signs corresponding to other notions. Iп what follows these two conventions are used: А letter enclosed in brackets, thus (х), denotes 'а persoп aged х'. А letter or numberenclosed iп а right angle, thus 7iJ or lsl, dt:пotes а term-certain ofyears. FUNDAMENTAL SYMBOLIC LETTERS Interest i = the effective rate of interest, пamely, the total interest earned on I in а year on the assumpti<;>n that the actual interest (if receivaЫe otherwise than yearly) is invested forthwith as it becomes due on the same terms as the original principal. INTERNATIONAL ACTUARIAL NOTATION 125 v = (1 +i)-1 = the present value of 1 due а year hence. d = 1 -v = the discount on 1 due а year hence. 3 = lo& ( 1 + i) = - lo& ( 1 -d) = the force of interest or the force of discount. Mortality ТаЬ!еS' l = number living. d = number dying. р = probaЬility of living. q = probaЬility of dying. µ = force of mortality. т = central death rate. а = present value of an annuity. S' = amount of an annuity. е = expectation of Iife. А = present value of an assurance. Е = present value of an endowment. Р} = prem~um per annum. Р generally refers to net premiums, ~т to special тт premшms. V = policy value. W = paid-up policy. The methods of using tl1e foregoing principal letters and their precise meaning when added to Ьу suffixes, etc., fo\1ow. Interest i<т> = т{(1+i) 1 fm_1} = the nomiпal 1·ate of interest, convertiЫe т times а year. ani = v + v2 + ... + v" = the valuc of an annuity-certain of 1 per annum for п years, tl1e payments being mad~ at the end of each year. 2 11 1 ап~ = 1 + v + v + ... + v - = the value of а similar annuity, the payments being made at the beginning of each year. 2 11 1 S'nJ = r + ( I + i) + ( r + i) + ... + ( 1 + i) - = the amount of an annuity-certain of 1 pcr annum for п years, the payments being made at the end of each year. sni = ( I + i) + ( I + i)2 + ., . + ( 1 +i)" = the amount of а similar annuity, the payments being made at the beginning of each year. The diaeresis or trema above the lette!"s а and s is used as а symbol of acceleration of payшcnts. Mortality ТаЫеs The ages of the lives involved are denoted Ьу letters placed as suffixes in the \o\ver space to the right. Thus: lж = the number of persons who attain age х according to the mortality tаЫе. dж = {" -!" ~ 1 = thc number of persons who die between ages х and х + r accordiг.g to the mortality tаЫе. Рж = the pl'ObaЬility that (х) will Iive 1 year. qж = the probaЬility that (х) will die within 1 year. 126 INTERNATIONAL ACTUARIAL NOTATION Р.х = - ~ ~; = the force of mortality at age х. тх = the central death-rate fo~ the year of age х to х + 1 = dx / f: lжн dt. ех = the curtate 'expectation of life' (or average after-lifetime) of (х). ln the following it is always to Ье understood (unless otherwise expressed) that the annual payment of an annuity is 1, that the sum assured in any case is 1, and that the symbols indicate the present values: ах= an annuity, first payment at the end of а year, to continue during the life of (х). iix = 1 +аж = an 'annuity-due' to continue during the life of (х), the first payment to Ье made at once. Ах = an assurance рауаЫе at the end of the year of death of (х). Note. ех =ах at rate of interest i =о. А letter or number at the lower left corner of the principal symbol denotes the number of years involved in the probability or benefit in question. Thus: пРх = the probaЬility that (х) wШ Iive п years. nqx == the probaЬility that (х) will die within п years. Note. When п = х it is customary to omit it, as shown on page 2, provided no amЬiguity is introduced. nEx == vnnPж = the valu'e of an endowment on (х) рауаЫе at the end of п years if (х) Ье then alive. If the letter or number comes before а perpendicular bar it shows that а period of deferment is meant. Thus: nlqx == the probaЬility that (х) will die in а year, deferred п years; that is, that he will die in the (п + 1 )th year. ~Jax == an annuity on (х) deferred п years; that is, that the first payment is to Ье made at the end of (п + х) years. nltax = an intercepted or deferred temporary annuity on (х) deferred п years and, after that, to run for t years. А letter or number in brackets at the upper right comer of the principal symbol shows the number of intervals into which the year is to Ье divided. Thus: а 1 ~ 1 = an annuity on (х) рауаЫе Ьу т instalments of i/m each throughout the year, the first payment being one of 1/т at the end of the first r/mth of а year.