Research

We construct a range of measures of social capital (the strength and structure of social networks) for the United Kingdom using data from Facebook covering 20.5 million adults. We make these measures publicly available. Low-socioeconomic-status (SES) individuals have far fewer high-SES friends than high-SES individuals do. Areas with more cross-SES friendships display higher levels of intergenerational economic mobility (higher adult earnings for children growing up in disadvantaged families). Most of the difference in connectedness to high-SES individuals between low- and high-SES individuals is due to differences in friending bias—the tendency of people to befriend others similar to themselves even conditional on the possible friends they are exposed to. Areas with more long ties (friendships between people with no mutual connections) also display substantially higher levels of intergenerational economic mobility, and long ties are especially likely to form outside the typical settings in which individuals make friends. The relationships between economic connectedness, long ties, and intergenerational economic mobility remain strong even after controlling for other area-level characteristics. We also make new estimates of intergenerational economic mobility in the UK publicly available, including the first estimates for areas in Scotland and Northern Ireland.

How is economics evolving as a discipline—are its subfields converging or fragmenting, and what drives the growth of new research areas? I construct a semantic map of ∼50,000 papers from 24 journals and NBER Working Papers (2000–2026) by embedding titles and abstracts into a continuous intellectual space using SPECTER2, a transformer model trained on scientific text. The map reveals a discipline that is specializing in place, not splintering apart: within-field homogeneity has increased substantially, yet the distances between fields have remained essentially unchanged. Compositionally, applied empirical fields have expanded while theoretical and financial clusters have contracted—the credibility revolution is visible in the data. Fields whose researchers and citations reach into intellectually distant areas tend to grow faster (ρ = 0.29 for author mobility, ρ = 0.41 for outgoing citations), while exchange between nearby fields does not predict growth. This asymmetry is consistent with recombinant growth models, in which the innovative potential of combining ideas increases with the distance between them. At the paper level, however, boundary-spanning papers do not earn a citation premium, suggesting the mechanism operates through the flow of researchers across intellectual borders rather than through individual interdisciplinary papers. An interactive version of the map is publicly available.