How can this possibly be justified: "To screen out business calls and casual calls, Dunbar and co include only individuals who make reciprocated calls and focu

How can this possibly be justified: "To screen out business calls and casual calls, Dunbar and co include only individuals who make reciprocated calls and focus on individuals who call at least 100 other people." I recall a recent joke about people who carry big book bags onto crowded New York City subways: your book bag is not a gateway to a hyper dimensional space outside of 3 dimensional reality, so please mind what you do with that damn bag, because it takes up a lot of space. Likewise, your business contacts take up a lot of space. They take time and energy and brainpower, the very thing that would limit the number of people that you can possibly keep track of. Therefore any attempt to exclude business calls invalidates the results.