Closing price of
Citigroup stock on
November 1, 2007
Closing price of
Citigroup stock on
November 7, 2007
Uninformed may
help democracy
Indifferent individuals can
help foster majority rule
By Susan Milius
Odd as it sounds, adding some wishy-washy members to a group can wrest
control from a strongly opinionated
minority and make collective decisions
more democratic.
At least that’s what happened in an
experiment with schooling fish and
three kinds of computer simulations
described in the Dec. 16 Science. The
study “supports a growing body of
evidence that larger groups are better
decision makers than smaller groups,”
says applied mathematician David
Sumpter at Uppsala University in Sweden, who studies collective behavior.
The fish study grew out of computer
simulations by Iain Couzin of Princeton
University demonstrating the consider-
able power of opinionated minorities
in otherwise indifferent groups, flocks
or herds. When he mixed factions with
different strengths of opinion in one
simulation, as well as in two very differ-
ent analyses of group behavior, he found
peculiar effects of uninformed parties.
Short spike suggestive of bear raid
Trading data suggest 2007 effort to manipulate share price
By Rachel Ehrenberg
Two extraordinarily large trading days
for Citigroup shares in the fall of 2007
hint that someone may have been
manipulating the stock, say researchers
from the New England Complex Systems
Institute in Cambridge, Mass.
The analysts were examining stock
trading data for the period January 2007
to January 2009 when they noticed two
unusually large spikes in volume and
other measures related to Citigroup
shares. On November 1, 2007, the team
noted, the number of borrowed Citigroup
shares jumped by 100 million, reach-
ing a value of $6 billion. Six days later, a
similar number of borrowed shares were
returned on a single day, the team reports
online December 14 at arXiv.org. The esti-
mated gain for investors who made the
transactions was at least $640 million.
