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National Institute of Population and Social Security Research

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Brief Summary

The Japanese Mortality Database was compiled based on HMD methodology. Below is an overview of HMD methodology.

  1. Birth numbers: Gather annual birth numbers split for gender for as long a period as possible.
  2. Death numbers: Gather as detailed as possible death numbers and when gathering raw data estimate number of deaths separated for age, year of death, year of birth, using a uniform method.
  3. Population Size: Estimate the population size on January 1 for every year, based on birth and death rates in the census or statistical data.
  4. Life Expectation against Risk (Exposure-to-risk): Estimate Life Expectation exposed to death risk for a given age x time period.
  5. Death rates: Death rate is calculated as a proportion of the number of deaths for a given age x time period against the corresponding life expectation.
  6. Life Chart: To create a life chart, first calculate the probability of death based on death rates.

For a more detailed explanation of the process, please see the Human Mortality Database website.

In the JMD we do not simply use the HMD methodology but we adapt it to fit the situation in Japanese mortality, within limits that do not prevent comparability. Below are the main changes:

  • We create a separate formula for estimating a0 using recent Japanese data.
  • We use Proportional distribution the standard population used in current population estimates of the Office of Statistics of the Ministry of Internal Affairs and Communications for unknown proportional distribution of age.
  • We use population data for birth month in the national census when estimating population size.
  • We made regional adjustments for return of Okinawa consist with Japanese demographic statistics.