Complementary use of the population census serves to show the family links within households and to define more exactly the reference person than with main use.
The rule for definition is as follows:
- If the household contains one or more than one family, including at least one with a couple, the reference person is the oldest active man or, failing this, the oldest man;
- Otherwise, if the household contains at least one single-parent family (and no family with a couple), the reference person is the oldest active person or, failing this, the oldest person;
- Finally, if the household contains no family, the reference person is, among the persons of the household except guests or accommodated employees, the oldest active person or, failing this, the oldest person.