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Force of mortality

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Force of mortality  (FORCE of mortality)


The differences between the number of survivors (431-4) at different ages give the number of deaths within the age interval or the death function1. The ratio of deaths between ages x and x + n to the number of survivors at age x is called the probability of death2 between ages x and x+ n. The central death rate3 is the ratio of deaths between ages x and x + n to the mean population alive at that age. The force of mortality4 or instantaneous death rate4 is the derivative of the natural logarithm of the survivorship function (431-3) taken negatively.

  • 1. The number of deaths between ages x and x + n is written ndx and between ages x and x + 1 is written dx.
  • 2. The probability of dying between age x and x + n is written nqx and between ages x and x + 1 is written qx.
  • 3. The central death rate at age x is written mx.
  • 4. The force of mortality at age x is written µx.


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