Figure 5

Pairs categorized into different subsets based on gender, frequency of contact and distance of separation. The coefficients α (basal value of call duration), β (strength of the dependence of the duration of the succeeding call on the logarithm of the inter-call gap) and \(\beta'\) (strength of the dependence, when both the duration and the gap are scaled by their respective averages) resulting from regression fits when pairs in \(\mathcal{S}\) (set of regular contacts) are categorized into different subsets. A broad distinction into four groups (as indicated on the top of the columns) is done based on whether for a given pair the distance between the most common locations (\(d_{ij}\)) is less or greater than \(d_{c}\) (i.e., geographically ‘close’ or ‘distant’, respectively) with \(d_{c}\) being the spatial extension of large cities; and whether average gap (\(\langle\tau\rangle_{ij}\)) is less or greater than \(\tau_{c}\) (i.e., communication is ‘frequent’ or ‘infrequent’) with \(\tau_{c}\) being the most probable inter-call gap. A finer classification is made based on the gender of the individuals as indicated along the horizontal axis. Pairs are chosen irrespective of their age. The dashed line is a guide to the eye. (See Additional file 1 for values without gender classification.)