Spatial patterns of close relationships across the lifespan

The dynamics of close relationships is important for understanding the migration patterns of individual life-courses. The bottom-up approach to this subject by social scientists has been limited by sample size, while the more recent top-down approach using large-scale datasets suffers from a lack of detail about the human individuals. We incorporate the geographic and demographic information of millions of mobile phone users with their communication patterns to study the dynamics of close relationships and its effect in their life-course migration. We demonstrate how the close age- and sex-biased dyadic relationships are correlated with the geographic proximity of the pair of individuals, e.g., young couples tend to live further from each other than old couples. In addition, we find that emotionally closer pairs are living geographically closer to each other. These findings imply that the life-course framework is crucial for understanding the complex dynamics of close relationships and their effect on the migration patterns of human individuals.

💡 Research Summary

The authors exploit a seven‑month mobile‑call dataset from a single European carrier, comprising roughly 1.9 billion calls among 33 million users, of which 5.1 million have associated age, sex and municipality information. For each “ego” they rank alters by total call volume, focusing on the top‑ranked and second‑ranked contacts. Only ego–alter pairs with complete demographic data are retained, yielding 1.1 million top‑ranked and 0.7 million second‑ranked dyads. A binary geographic difference index hᵢⱼ is defined (0 = same municipality, 1 = different).

The analysis separates dyads by (i) sex combinations (F:F, M:M, F:M, M:F) and (ii) age difference ≤10 years (potential peers or partners) versus >10 years (potential inter‑generational ties). The average hᵢⱼ is plotted as a function of ego age. For opposite‑sex dyads with small age gaps, hᵢⱼ rises to about 0.7 around age 20, then declines to ~0.45 by the mid‑40s and stabilises thereafter. The authors interpret this as young couples living apart during education or early career, later co‑habiting as they age. Same‑sex dyads show a clear sex effect: male‑male pairs consistently have lower hᵢⱼ than female‑female pairs, indicating that men’s closest same‑sex friends tend to live nearer.

When the age gap exceeds ten years, sex differences vanish. Here hᵢⱼ peaks in the 30s, dips around the mid‑40s, and rises again for older egos, a pattern the authors link to children leaving the parental home after the early‑20s.

Further, the authors examine the distribution of alter ages for specific ego age groups (25, 40, 60) and find that alters of similar age are more likely to be geographically close, while peaks at ages ~20 (children) and ~30 (parents) appear for older egos, supporting the inter‑generational interpretation.

Extending beyond the top two alters, the study constructs ego‑centric networks ordered by call frequency. The geographic difference index increases monotonically with alter rank, confirming that stronger (more frequently called) ties are on average geographically nearer. Sex‑specific patterns emerge: 25‑year‑old women call more distant alters than men of the same age, whereas the reverse holds for 40‑year‑olds; the distinction disappears at 60.

Robustness checks using province‑level aggregation and distance thresholds of 10 km and 50 km yield qualitatively identical results.

In discussion, the authors acknowledge three core assumptions: (1) call frequency proxies emotional closeness, (2) small age‑difference opposite‑sex top alters represent partners, and large age‑difference alters represent parent‑child ties, (3) life‑course migration is reflected in the observed age‑sex‑geography patterns. Under these premises they conclude that (a) young couples tend to live farther apart than older couples, (b) women’s same‑age, same‑sex close contacts are geographically more dispersed than men’s, (c) inter‑generational ties exhibit similar geographic patterns regardless of sex, and (d) emotionally closer friends are generally physically nearer, challenging the notion that phone calls primarily compensate for distance. The work demonstrates how large‑scale digital trace data, when combined with limited demographic information, can illuminate the interplay between social relationships and migration across the human lifespan.