  Decisions in a group often result in imitation and aggregation, which are
enhanced in panic, dangerous, stressful or negative situations. Current
explanations of this enhancement are restricted to particular contexts, such as
anti-predatory behavior, deflection of responsibility in humans, or cases in
which the negative situation is associated with an increase in uncertainty. But
this effect is observed across taxa and in very diverse conditions, suggesting
that it may arise from a more general cause, such as a fundamental
characteristic of social decision-making. Current decision-making theories do
not explain it, but we noted that they concentrate on estimating which of the
available options is the best one, implicitly neglecting the cases in which
several options can be good at the same time. We explore a more general model
of decision-making that instead estimates the probability that each option is
good, allowing several options to be good simultaneously. This model predicts
with great generality the enhanced imitation in negative situations. Fish and
human behavioral data showing an increased imitation behavior in negative
circumstances are well described by this type of decisions to choose a good
option.
