Dr David McGrath

Spine Physician

MB BS (Hons) FAFOM, RACP, FAFMM
Master of Pain Medicine

Is the crowd right? Why is the prevailing view so seductive?
Let's look at the maths.

ViewpointTruth	True	False
Crowd View, Positive	a	b
Crowd View, Negative	c	d

The "a" cell represents a correct view of a true situation
The "b" cell represents incorrect view of a false situation
The "c" cell represents an incorrect view of a true situation.
The "d" cell represents a correct view of a false situation

Let's consider an evolutionary example. In the jungle we need to distinguish predators. Consider an environment with 200 disturbances half of which are due to tigers. If a tiger is sensed a vocalisation spreads to other members of the troup. By this method the troup can all act in a defensive manner. In other words all the members behave consensually and their success may be large.

ViewpointTruth	True,Tiger Present	False, No Tiger Present
Crowd View ,Positive Defence	99	99
Crowd View ,No Defensive Position	1	1

In this example, the troup are wrong half the time, but their success as measured by a/c is 99%.
Lets compare that result with the judgement of an individual.

ViewpointTruth	True,Tiger Present	False,No Tiger present
Individual View ,Positive Defence	1	1
Individual View, No Defensive Position	99	99

Here the numbers are reversed. The ability to detect a tiger is still 50%, but the overall success is only 1%.

Under these circumstances it would be far wiser to accept the collective judgement of the crowd.

Under what circumstances does this ideal decision making process fail?
The success of a collective lies in the aggregation of seperate usuful pieces of information. In the above example,each member contributes their sensory capacity to a larger social structure. The sensitivity to detect a tiger is increased by each member of the troup. When sensitive decisions are needed this is truely an advantage.
The crowd is not wise when the independence of the members is destroyed by other forces such as leadership,coercian or channelled information flow.
In medicine, for example,there can be influential articles that persuade a large percentage of people to a particular view. Exams in colleges narrow the focus, often demanding the "status quo" answer.
People may read the same journals or texts. Sharing an understanding in essence means acting in the same manner. All this points to reduced data points and not independant input.
The contingency table starts to revert to the single observer. Science is aware of social bias of this nature and has developed techniques to get around the difficulty. Carefully controlled experiments try to aggregate independant information to reach the best conclusion.
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