2. • Assumption of life table
1. The cohort is closed. No migration, No birth, only deaths
occur
2. People die according to schedule (fixed)
3. Cohort originate as 1,000, 10,000, 100,000, 1,000,000 called
‘radix’
4. At each age (except first few year of life) death are evenly
distributed between one birth day and next birth day
5. Life table for male and female
• Two type of life table
1. Complete life table (each year)
2. Abridged life table (age group / interval – 5 or 10 year)
3. • Symbols used in life table (Conventional notations)
1. Radix : Some standard number of birth (cohort) like 1,000,
10,000, 100,000
2. x : The age attained at last birth
3. nLx : Number of person-year lived between age x and x+n
4. nqx : Probability of dying between age x and x+n
5. npx : Probability of surviving between age x and x+n
6. ndx : Number of death between age x and x+n
7. nmx: Age specific death rate for age group x and x+n
8. Tx : Total number of person-year lived after age x
9. ex: Expectation of life at age x
10. lx : Number of survival at age x
4. • Some interrelationships between the function of a stationary
population
• nqx = 1 – npx
• nqx = ndx/lx
• ndx= lx .nqx
• nLx= (n /2) (lx + lx+ n )
• nmx = ndx / nLx
• nqx= 2n. (nMx) / [2 + n. (nMx)]
