## Life Table Columns and Their Definitions **Key Point:** The dx column in a life table represents the **number of persons dying during a specific age interval**, calculated as the difference between lx (survivors at the start of the interval) and l(x+n) (survivors at the start of the next interval). ### Understanding Life Table Components | Column | Symbol | Definition | Formula | |--------|--------|------------|----------| | Survivors at start of interval | lx | Number alive at age x (out of radix, typically 100,000) | — | | Deaths during interval | dx | Number dying between age x and x+n | lx − l(x+n) | | Probability of death | qx | Probability of dying in the interval | dx / lx | | Person-years lived | Lx | Total years lived by cohort in interval | (lx + l(x+n)) / 2 | | Total person-years remaining | Tx | Sum of Lx from age x onwards | Σ Lx | | Life expectancy | ex | Average years remaining at age x | Tx / lx | **High-Yield:** The relationship is: **dx = lx − l(x+n)**. This is the absolute number of deaths, not a probability or rate. ### Clinical Pearl In a life table with a radix of 100,000 (standard in India and most countries), if lx = 95,000 at age 20 and l(x+5) = 94,500 at age 25, then dx = 500 persons died in that 5-year interval. **Mnemonic:** **dx = Deaths in interval** — the 'd' stands for deaths, and it is an absolute count, not a proportion.
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