CFM vs UDD vs Balducci

Life Tables:
It is a computational tool based on a specific survival model. Our task is to generate a survival model and our output will be a life table. Life table is based on Unitary method.
lx = Expected no. of lives at age x
dx= Expected no. of deaths between exact age x and exact age x+1
NOTE: We call it expected and not actual because most of the values will be in decimal too, so how can it be actual.

But there is a limitation of Life Tables: It is defined only for integer ages. If we have to calculate probability of death/survival at any non-integer age we will use 3 assumptions:
1.CFM= Constant Force of Mortality
2.UDD= Uniform Distribution of death
3.Balducci assumption

·       It assumes that the force of mortality is constant, i.e. ux+t = ux
·       If the force of mortality of a newborn is constant, it means that the expected future lifetime of this life is 1/μ no matter what age he is in.
·       Survival Function in this case will decrease exponentially.
·       If 0<s<t<1 then t-spx+s = tpx/spx = (px)t-s

·       It assumes that force of mortality increases between integer ages and here tqx = t.qx  where 0<t<1
·       It assumes that deaths are uniform over a period of time. For ex: There are 24 deaths in a year then it means there are 2 deaths in a month or 1 death in every 15 days.
·       It assumes that PDF of Tx to be constant if it follows uniform distribution.
·       Survival Function in this case will decrease linearly.
·       If  0<s<t<1 then t-sqx+s  = [qx(t-s)]/[1-s.qx]

·       Here force of mortality decreases between integer ages and assumption is 1-tqx+t = (1-t)qx
·       It means that mortality is heaver in the first half of the year than it is in the second half.
·       The force of mortality decreases in late teenage years/early twenties, so the Balducci assumption may be more appropriate there. Look at the values for mu in the AM92 tables.
·       If 0<s<t<1 then t-sqx+s = [qx(t-s)]/[1-(1-t)qx]

Now let’s see the human mortality graph:

·       You can see here the hump between ages 15 -20 years of age. This effect is called the "accident hump", which is described in CT5. Basically, mortality comes to a small peak around 17/18/19, and then decreases. The peak is usually associated with deaths from car accidents of inexperienced drivers, and drug/alcohol-related deaths.

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But there is something more related to mortality:

Gompertz and Makeham Laws of Mortality:

Gompertz law is an exponential function and it is often a reasonable assumption for middle ages and older ages. Formula is ux = Bcx. Now we say that it is a reasonable assumption between 35-65 years of age because if we take the log of the equation i.e logux= logB + xlogc , then we can see that increase in rate of mortality with age is constant which is often a reasonable assumption.

Makeham law formula is ux= A+Bcx. It incorporates a constant term, which is sometimes interpreted as an allowance for accidental detahs, not depending on age.

Gompertz and makeham family curves equation is (polynomial{1})+exp(polynomial{2})

Initial and central rates of mortality

qx = is called initial rates of mortality, because it is the probability that a life alive at exact age x dies before the exact age x+1

mx = is the probability of dying between exact ages x and x+1 per person year lived between exact ages x and x+1

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Follow me on LinkedIn: Kamal Sardana


  1. Nice post,thanks for giving this post this is very useful to every one and like this types also good explanation.thank you
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