Social capital I: measurement and associations with economic mobility

Building on previous work, we organize measures of social capital into three categories: (1) cross-type connectedness, which is the extent to which different types of people (for example, high income versus low income) are friends with each other; (2) network cohesiveness, which is the degree to which friendship networks are clustered into cliques and whether friendships tend to be supported by mutual friends; and (3) civic engagement, which we measure using indices of trust or participation in civic organizations.

Cross-type connectedness can be viewed as a form of ‘bridging’ capital, whereas network cohesiveness is more in line with the concept of ‘bonding’ capital. In addition to measuring distinct concepts, these categories of social capital differ in terms of the data they use as inputs. Measures of cross-type connectedness combine data on networks (friendship links) with data on individual characteristics. By contrast, measures of cohesiveness use only data on network links, with no characteristics. Finally, measures of civic engagement do not use data on networks at all and are instead based purely on individual or community-level characteristics (Supplementary Table 6).

We measure these concepts, which are defined more precisely below, using privacy-protected data from Facebook (Methods: ‘Sample construction’ and ‘Privacy and ethics’). We focus on Facebook users with the following attributes: aged between 25 and 44 years who reside in the United States; active on the Facebook platform at least once in the previous 30 days; have at least 100 US-based Facebook friends; and have a non-missing residential ZIP code. We focus on the 25–44-year age range because its Facebook usage rate is greater than 80%. On the basis of comparisons to nationally representative surveys and other supplementary analyses, our Facebook analysis sample is reasonably representative of the national population (Methods: ‘Benchmarking’). We use the Facebook data to obtain information on friendships, locations (ZIP code and county), and individuals' SES and their parents' SES. These variables are described in detail in the Methods (‘Variable definitions’).