  Understanding tie strength in social networks, and the factors that influence
it, have received much attention in a myriad of disciplines for decades.
Several models incorporating indicators of tie strength have been proposed and
used to quantify relationships in social networks, and a standard set of
structural network metrics have been applied to predominantly online social
media sites to predict tie strength. Here, we introduce the concept of the
"social bow tie" framework, a small subgraph of the network that consists of a
collection of nodes and ties that surround a tie of interest, forming a
topological structure that resembles a bow tie. We also define several
intuitive and interpretable metrics that quantify properties of the bow tie. We
use random forests and regression models to predict categorical and continuous
measures of tie strength from different properties of the bow tie, including
nodal attributes. We also investigate what aspects of the bow tie are most
predictive of tie strength in two distinct social networks: a collection of 75
rural villages in India and a nationwide call network of European mobile phone
users. Our results indicate several of the bow tie metrics are highly
predictive of tie strength, and we find the more the social circles of two
individuals overlap, the stronger their tie, consistent with previous findings.
However, we also find that the more tightly-knit their non-overlapping social
circles, the weaker the tie. This new finding complements our current
understanding of what drives the strength of ties in social networks.
