Social network
A socio‐centric family network was constructed among HITS‐eligible individuals using routinely collected surveillance data. Nodes in this network represent individuals. Three kinds of ties were added between the nodes: first‐degree relatives (parents, children and all conjugal partners of each participant), second‐degree relatives (the first‐degree relatives of first‐degree relatives) and co‐resident relatives (individuals who ever resided in the same household as the participant and who were not tenants or domestic workers in that household). Below, we refer to members of each person's personal family network (i.e. the egocentric network) simply as “family members.”Family members of residents are only recorded if they ever resided in the surveillance area. For most individuals, it was possible to identify at least one family member—only 2.7% (424/15,675) of HITS participants were not linked with any other residents. Because surveillance began in 2000, older residents were less likely to be observed at the same time as their parents. Among the records of individuals aged 15–25, 15.0% (2321/15,458) were not linked to their mother's record and 48.3% (7471/15,458) were not linked to their father's. Among those over 55 years of age, these proportions were 87.9% (4795/5458) and 97.3% (5310/5458), respectively. Missing linkages between participants and their parents indicate that their parents were not eligible for the study.