The number of years is calculated from the year the person moved to the residence. For individuals surveyed in 2008 declaring they moved in 2008, the number of years is 0; for those who declared 2007, the number of years is 1, etc.
If all the occupants present for the census did not arrive at the same time, the moving date corresponds to that of the person who arrived first. If that person has always lived in the residence, the moving year corresponds to his/her year of birth.