The chart shows the average age of migrants in 2011. Average age has been computed as the average of migrants of each age divided by the total number of years of age they represent altogether. The migrants’ age is derived from a variety of statistical estimation methods carried out by national statistical institutes and validated by Eurostat. Most MS use administrative sources for compilation of migration data (population register, register of foreigners, database on residence permits issued, etc). Immigrants are usually registered either at the point of entry into the MS or the Schengen zone, or at the location of their residence, making it relatively easy to record information about their citizenship. The recording of emigrants, on the other hand, relies on their deregistering from the authority of their place of residence at the time of leaving, and is thus prone to under-recording.