Demography

1. A life table is designed essetially
to measure mortality. It is a
statistical model from which the
measure of mortality are derived.

2. It represents the mortality
experience in a series of years,
based on an individual's year of
birth and the year in which they
reach each succeeding age.
This life table represents the
combined mortality experience
by age of the population in a
particular short period of time.
Hence it is viewed as snapshot of
current mortality.
It contains data of every single
year of age from birth to the last
applicable age. It is also called
unabridged life table
TYPES
2

3. Types
3
Abridge table contains the data
by intervals of five or ten-years,
except in the initial years. This is
the abridged life tables that most
users frequently encounter
In this life table only one cause of
death and only one characteristic
are considered at a time, and are
concerned with general
experience of a cohort by age.
This table described the separate
and combined effects of more
than one characteristic; it may
consider more than one cause of
death and or more than one
characteristic at a time.

4. 4
1 2 3 4 5 6 7 8
x Ix dx qx px Lx Tx ex
0
• x = Age in years
• Ix = No. of persons living at an specified age
• dx = No. of persons among the lx persons who die before reaching the age x+1
• qx = Probability that a person of age x will die within one year
• Px = Probability that a person of age x will survive till his next birthday
• Lx= The total no. of persons living between the age x and x+1
• Tx = Total future lifetime of Ix persons who reach x years
• ex
0 = The avg. no. of years a person of age x is expected to live

5. 5
X
• Number of death dx is the number among the survival at age x persons who died before
reaching the (x + 1) , that is
x
• Mortality rate qx is the probability the person at exact age will die with one year
following of that age, this is obtain as follows.
qx = dx / lx
• Person-years lived Lx the number of year lived in the aggregate by the cohort lx persons
between exact age x and exact age X + 1 of persons alive at age x.
Lx = lx – 0.5dx
dx = lx – lx+1
• Persons-years lived after x ( Tx ) : This implies the number of years lived by the cohort lx
after attaining the age x.
Tx = Lx + Tx+1
• The average no of years a person of age x is expected to live ex
0
ex
0 = Tx / lx
• px is the probability of survivorship which implies the probability that person aged x is surviving
up to his next birthday (x + 1) which is
px = lx+1 / lx
x
lx