The Lifelines cohort consists of a lot of family relationships. During the inclusion participants were specifically asked if they had any family members who would be intereseted in joining the cohort. This has developed Lifelines into one of the largest 3 generations cohort available.

The basis of the family relations data within Lifelines consists of information from the municipal registries (Basisregistratie Personen (BRP)). Based on this information, researchers from the UGLI-consortium have optimized the family relations using recoded surname data (for privacy purposes) and data from questionnaires (Family composition). The process of this optimization has been documented and can be found here: Family relations reconstruction

In the latest version of the family relations data couples who share a household, but don't have children, have also been included. This provides the opportunity to work on research involving environmental factors.

The data consists of 5 columns:

• Participant identifiers
• Family id
• Father identifier
• Mother identifier
• Gender
• Partner identifier

The identifiers can be used to pair the family data to other phenotypic and genotypic data. The same participant identifier can also be found in the column for father or mother and partner. This depends on the participant's family size. Participants who have indicated to have family members who are not participating in Lifelines have also received a unique identifier, but this identifier can not be used to pair the data to other Lifelines data. An example of this is when two siblings have indicated to have the same father. The identifiers of these family members, who are not participating in Lifelines, start with an 'S' (i.e. S1031206). The family id is used to identify participants that are part of the same family.