- lx: It is the number of surviving lives alive at exact age 𝑥.
- 𝑑𝑥: It is the number of deaths over the year of age 𝑥.
- qx: Probability of dying in year x
- px: Probability of surviving year x
1. l𝑥+1=𝑙𝑥−𝑑𝑥: It means the number of surviving person at age x+1 is equal to the number of surviving person at age x minus total deaths in year x
2. 𝑞𝑥=𝑑𝑥/𝑙𝑥: It means the number of deaths in a year divided by number of person living at age x
3. 𝑝𝑥=(𝑙𝑥+1)/lx: It means the probability of surviving is equal to the number of people alive in year x +1 divided by the number of people died in the year x
4. px = 1-qx: It means that the probability of surviving is equal to 1 minus probability of death. In other words, the probability of surviving and probability of death equals 1
Collectively, 𝑙𝑥, 𝑑𝑥, 𝑞𝑥 and 𝑝𝑥 form what is called a “life table” or “actuarial table”.