The sizes of the entire ego networks for the three data sets are smaller than the total size of conventional offline egocentric networks (typically about 150 alters: Hill and Dunbar, 2003, Roberts et al., 2009). This is true especially for the Facebook data sets, where the most external ego network layer is completely missing. This is, perhaps, not too surprising, since the outermost (150) layer in offline networks corresponds to people who are contacted only about once a year. At least as far as the Facebook data sets are concerned, early users (remember that data sets were collected in 2009, when Facebook was still new and yet to start its exponentially increasing diffusion) were not forced into ‘friending’ complete strangers and, instead, typically only sought out people they knew well. Moreover, as discussed earlier, the information we have about weak relationships in Facebook data sets could be not enough to identify all the relationships with very low contact frequency.