&gt; The team also finds some evidence of an extra layer among some people. “This could, for example, mean introverts and extroverts have a different number of layers of friends,” they suggest. But interestingly, extroverts, while having more friends, still have a similar number of layers.<p>&gt; In total, the study shows good evidence for the existence of the innermost and outermost layers but with some variability for the size of the intermediate layers. “The clustering yields results that match well with previous studies for the innermost and outermost layers, but for layers in between we observe large variability,” they say.<p>I was curious about those comments in the BBC article, so I took a look at the paper and found this from the conclusions useful:<p>&gt; While the data is noisy, all
methods support two different groupings well. This
could, for example, mean introverts and extroverts
have a different number of layers of friends. Further
work could investigate this possibility.<p>&gt; Another suggestion
is that over a year, friendships are more transient.
Alters could move up or down from one layer
to the next on a regular basis. This would reflect the
temporal nature of emotional closeness, especially
among one’s non-closest friends