The survey population comprises all people in the Netherlands aged between 30 and 35 on 1 January 2011. The demographic profile of this group is monitored since their 15th birthday. Important events in this respect are the moment of leaving the parental home, the moment they start living on their own, the moment they start living together with a partner for the first time (married or not married) and further steps affecting their marital status and household position. The parents of this group are only surveyed with respect to first and next marriages. Collection of these data is fairly easy because for people belonging to that generation living together without being married was rare.
The initial population comprised 502 thousand women and 504 thousand men born between 1976 and 1980. Only native men and women born in the Netherlands were selected, i.e. native Dutch and second-generation people with a foreign background, because only these data files are complete. If parents have more than one child participating in the survey, one daughter per mother and one son per father were randomly selected. The survey population eventually included 359 thousand women and 372 thousand men.
The age, at which women start living together for the first time is compared to the age of their mothers when they first married; the age, at which men start living together for the first time is compared to the age of their fathers when they first married. The age at marriage of the mothers and fathers was categorised as follows:
younger than average 20 yrs or younger 22 yrs or younger
average 21 or 22 yrs 23 or 24 yrs
older than average 23 yrs or older 25 yrs or older