The population census is used as a base for annual population estimates.

It is the only source which provides exact details of the population by gender and age at the different geographical levels.

Between two censuses, or pending availability of the data from the census of the year in question, population level and distribution are estimated. When the results from a new census become available, estimates that have already been made are revised to take these into account.

They then become definitive.

The breakdown of the population by age is based on age in completed years at 1 January of the year in question.

Method for estimating national population and distribution by gender and age

At national level, the population and its distribution by gender and age are estimated by updating the last available population pyramid with the civil status statistics relating to births and deaths by gender and age, and with an estimate of net migration by gender and age.

Birth and death statistics are obtained from information given to INSEE by the town halls.

Net migration, the difference between those entering and those leaving the territory, is measured indirectly as the difference between the change in population level between two successive years and the natural balance and any statistical adjustments.

Method for estimating regional and departmental populations and their distribution by gender and age group

At regional and departmental levels, net migration is often a larger component of the population trend than at national level, especially as at these levels, it also includes internal migrations between the different departments of France.

There is not enough statistical information available to give a sufficiently robust estimate for net migration at departmental or regional level.

Thus the methodology used at national level cannot be broken down and applied to these other geographical levels.

Firstly, the population at departmental and regional levels is estimated globally. Civil status statistics provide the natural increase at these levels.

For net migration, using previous population censuses an apparent net migration can be calculated by subtracting the natural increase from the population change (and any statistical adjustments) .

The observed trends are then extended.

Finally, an adjustment is made so that the population for all the departments or regions coincides with the national population estimate.

Secondly, the population at departmental and regional levels is distributed by age group, using civil status statistics by gender and age group and extending the observed trends across the migratory flows by gender and age group with the population censuses.