That any two persons are separated by a relatively small number of intermediary contacts -- the "small-world" phenomenon -- is a surprising but well established regularity in human social networks. To date, network science has ignored the question of whether the small world phenomenon manifests itself in similar ways across dyadic classes defined by individual traits, such as age or sex. To address this gap in the literature, we explore the phenomenon of "age-specific small worlds" by employing a mobile phone network built from billions of communication events approximating interaction patterns at a societal scale. We observe the average distance between any pair of users is 9.52, corresponding to nine-and-a-half degrees of separation. More importantly, we show that there is a systematic relationship between age and the average distance connecting that person to others, with some age groups falling below this average quantity while others falling above. Young people live in the "smallest world," being separated from other young people and their parent's generation via a comparatively small number of intermediaries. Older people live in the "least small world," being separated from their same age peers and their younger counterparts by a relatively large number of intermediaries. Middle age-people fall in between, being sociometrically close to both younger and older generations. However, there exists no significant difference of this age-effect on small world size between men and women. In all these results demonstrate that age-group heterogeneity of the small world can be traced to well-known social mechanisms affecting the way that age interacts with overall volume of connectivity and the relative prevalence of kin ties and non-kin ties, and may have important implications for our understanding of information cascades, diffusion phenomena, and the localized spread of fads and fashions.
['Yuxiao Dong', 'Omar Lizardo', 'Nitesh V. Chawla']
Do the Young Live in a "Smaller World" Than the Old? Age-Specific Degrees of Separation in a Large-Scale Mobile Communication Network