Persistence of social signatures in human communication

Abstract

The social network maintained by a focal individual, or ego, is intrinsically dynamic and typically exhibits some turnover in membership over time as personal circumstances change. However, the consequences of such changes on the distribution of an ego's network ties are not well understood. Here we use a unique 18-mo dataset that combines mobile phone calls and survey data to track changes in the ego networks and communication patterns of students making the transition from school to university or work. Our analysis reveals that individuals display a distinctive and robust social signature, captured by how interactions are distributed across different alters. Notably, for a given ego, these social signatures tend to persist over time, despite considerable turnover in the identity of alters in the ego network. Thus, as new network members are added, some old network members either are replaced or receive fewer calls, preserving the overall distribution of calls across network members. This is likely to reflect the consequences of finite resources such as the time available for communication, the cognitive and emotional effort required to sustain close relationships, and the ability to make emotional investments.

Keywords: personal relationships; quantitative sociology.

Fig. 1.

Social signatures and network turnover. (A and B) Social signatures are constructed for each ego by counting the number of calls to each of his or her alters, ranking the alters based on this number, and then calculating the fraction of calls to the alter of each rank. (C) When the signatures are averaged over the set of participants for three consecutive 6-mo intervals, it is seen that their shape is invariant although the personal networks display high turnover as indicated by the Jaccard indexes between sets of 20 top-ranking alters in consecutive intervals (Inset). In D, the network turnover is also clearly visible, which shows the total numbers of calls by the participants to their alters, divided between alters that have for the first time appeared in their networks in each of the intervals.

Fig. 2.

Individual-level variation in social signatures and their evolution. Upper (A–C) and Lower (D–F) depict the time evolution of the social signatures of two different male participants who both went to university in another city. The symbols correspond to alters observed for the first time in intervals I₁ (circles), I₂ (squares), and I₃ (diamonds) or to kin (triangles) as reported by the egos. The large turnover in the networks of the participants is clearly visible. The dashed line indicates the social signature averaged over all 24 egos. In the social signatures depicted in A–C, two kin alters receive a higher-than-average fraction of outbound calls, whereas the signatures D–F do not deviate much from the average. In both cases, this individual-level variation persists through all time intervals.

Fig. 3.

Evidence for the persistence of social signatures at the individual level, in terms of distances between the shapes of signatures. (A) A schematic of how the distances between signatures are calculated, based on Jensen–Shannon divergences. For the focal ego (Upper), self-distances d_self are calculated for signatures in consecutive intervals and averaged. Reference distances d_ref are calculated for each interval between the signatures of the focal ego and all other egos (Lower). These are averaged over the three intervals for each pair of egos (focal, other). (B) The values of the average self-distances d_self and histograms for reference distances d_ref for four sample egos, indicating that the shapes of each ego’s signatures in consecutive intervals are typically more similar than they are to those of other egos. (C) The distributions of all self-distances d_self and reference distances d_ref, for all egos, verifying the larger similarities between egos’ signatures in consecutive intervals. (D) The self-distances d_self show a moderate level of correlation (r = −0.41, P = 0.0034) with turnover as measured with the Jaccard index J, but nevertheless mostly remain below reference distances. The scatter plot shows the coordinate pairs and for each ego i (circles). For comparison, reference distances are also displayed as the coordinate pairs and . Solid and dashed lines denote the median and the quartiles.