This article presents the importance of preserving the possibility of comparing phenomena over time. The historical continuity of data makes it possible to follow the evolutions that are taking place in human societies and helps prevent changes, given the interaction of phenomena with the current conjuncture and historical context. The possibility of reconstructing the same family structures had been derogated in the 1998 census, by establishing a double definition of the house members. The possibility of reconstruction was made by the 2008 census. The "adopted children" modality was not present in the post censuses of 1996. This wil had a risk of having tiring phenomena in the society.