The Availability Heuristic and the Representativeness Heuristic

People often find themselves in situations where it is necessary to employ statistical
reasoning to solve problems or make intelligent estimates. The study of “social
cognition” has shown us that many people have difficulties using statistical information
effectively and they will often use other “heuristics” to help them solve problems.
Heuristics are shortcuts that we use to solve everyday problems- often they help us
make reasonable estimations.  Sometimes though, we rely on these shortcuts too
heavily and discard other pertinent information too readily. Two psychologists by the
names of Kahneman and Tversky studied these heuristics in depth by measuring
people’s performances on carefully devised tests. They wanted to see what rationale
people used to make decisions, especially decisions related to determining the
relative frequency of specific events. Two of the heuristics that they found were the
representativeness heuristic and the availability heuristic.

The representativeness heuristic is used when we judge two things as being similar
only because they share prima facie characteristics, or a superficial resemblance.  
People using this heuristic ignore statistical rules and assume that if one concept
shares a specific quality with another concept that these two concepts are sure to
share many other qualities, and should be categorized together.  This heuristic is
thought to be responsible for why many people see illusory relationships in series of
random events.  Also, the representativeness heuristic, when applied incorrectly, is
known to lead to the creation of very damaging stereotypes.

For example pretend that in the past you had a very unreliable car that had a long
antenna.  It is possible that while shopping for a new car you will encounter a car with an
antenna that is very similar to your old one.  If you find that you are biased against cars
with that type of antenna- without first taking into consideration the model, make and
specifications of the new car- you are probably using the representativeness heuristic.

The availability heuristic is similar but a little different.  Many psychological experiments
have shown that people regularly use easily accessible memories to make judgments
about the likelihood of events. This is probably because it is natural for us to use
concepts that readily spring to mind rather than complete and unbiased information.
We can easily remember recent experiences or reports from friends and the news, and
we often use these types of information instead of using statistical information to
estimate probabilities.

After hearing from a friend about the unreliability of a certain car, a listener using the
availability heuristic is likely to discard previous statistical knowledge about the car and
be biased against the car. This may occur even if the car is renowned for its
dependability. The new information creates an unrealistic bias against the car by
increasing the accessibility of the prejudiced information.

Heuristic: noun
A formula or series of steps that is used as a guide to solve a problem.  A time saving
algorithm or short cut- often speculative.

Prima Facie:   adv.
At first sight; before closer inspection. True, authentic, or adequate at first sight;