Average Path Length = (ln N / ln K) where N = desired number of nodes and K = mean degree (i.e., acquaintances per node; assumed to be an even integer). Thus if N = 6,000,000,000 (90% World pop.) and K = 30 then Degrees of Separation = 22.5 / 3.4 = 6.6. (Assume 10% of population is too young to participate.)
Duncan J. Watts, Steven Strogatz
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