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Revision of Method for Estimation
Japan's population is grasped in detail through the Population Census every five years, Population Estimates are published in order to grasp population of every month and year for the intercensal period.
The Base Population of the Population Estimates is changed from the population by the 2010 Population Census to that by Preliminary Count of the 2015 Population Census and also the method for the estimation is revised .
1 Changing the Base Population
The Base Population of the Population Estimates is the one from the most recent Population Census. The Base Population is revised every time after the operation of the Population Census.
From March 2016, the Base Population of the Population Estimates is changed from the population by the 2010 Population Census to that by the Preliminary Count of the 2015 Population Census tracing back to October 1, 2015
2 Revision of Method for Estimation
All Japanese migrants whose period of intended stay in foreign countries within 90 days (= the estimation by transients) has been included in the estimation of the migrational change, so it has a lot of seasonal fluctuation. We revised the method for the estimation by calculating Japanese exits of transients abroad every month and excluding them from Japanese migrational change, so as to change the Base Population from all Japanese migrants to "those who stay abroad for 91 days or longer". By this revision the Population Estimates become seasonally more stable. The revised Population Estimates are released from January, 2007 (Provisional Estimates as of January 1, 2007, and Final Estimates as of August 1, 2006).
Additionally, the latest estimates are released one month later than current method because of the data availability. And the retroactively estimated results since October 1, 2003 are also released for reference.
Foreign migrants whose intended period of stay in Japan is less than three months have been excluded since the revision of the Immigration Control and Recognition Act in July 2012, and at the same time, Japanese transient migrants whose period of stay abroad is less than three months also became excluded.