  We analyze a large-scale mobile phone call dataset containing information on
the age, gender, and billing locality of users to get insight into social
closeness in pairs of individuals of similar age. We show that in addition to
using the demographic information, the ranking of contacts by their call
frequency in egocentric networks is crucial to characterize the different
communication patterns. We find that mutually top-ranked opposite-gender pairs
show the highest levels of call frequency and daily regularity, which is
consistent with the behavior of real-life romantic partners. At somewhat lower
level of call frequency and daily regularity come the mutually top-ranked
same-gender pairs, while the lowest call frequency and daily regularity are
observed for mutually non-top-ranked pairs. We have also observed that older
pairs tend to call less frequently and less regularly than younger pairs, while
the average call durations exhibit a more complex dependence on age. We expect
that a more detailed analysis can help us better characterize the nature of
relationships between pairs of individuals and distinguish between various
types of relations, such as siblings, friends, and romantic partners.
