  In this paper, we introduce a geometric statistic called the "sprawl" of a
group with respect to a generating set, based on the average distance in the
word metric between pairs of words of equal length. The sprawl quantifies a
certain obstruction to hyperbolicity. Group presentations with maximum sprawl
(i.e., without this obstruction) are called statistically hyperbolic. We first
relate sprawl to curvature and show that nonelementary hyperbolic groups are
statistically hyperbolic, then give some results for products, for
Diestel-Leader graphs and lamplighter groups. In free abelian groups, the word
metrics asymptotically approach norms induced by convex polytopes, causing the
study of sprawl to reduce to a problem in convex geometry. We present an
algorithm that computes sprawl exactly for any generating set, thus quantifying
the failure of various presentations of Z^d to be hyperbolic. This leads to a
conjecture about the extreme values, with a connection to the classic Mahler
conjecture.
