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22 How people make decisions involving multiple objectives
very poorly on others. Research by Shafir 9 suggests that, if the decision
is framed as ‘which candidate should be selected?’, then most people
would select B. A selection decision will cause people to search for
reasons for choosing a particular candidate and B’s excellent communication
skills, very good absenteeism record and excellent computer skills
will provide the required rationale. If instead the decision is framed as
‘which candidate should be rejected?’ then, again, most people would
choose B – this candidate’s poor interpersonal, numeracy and telephone
skills will provide the necessary justification. Hence positive features
are weighted more highly when selecting and negative features more
highly when rejecting. This violates a basic principle of rational decision
making that choice should be invariant to the way the decision
is framed.
Another principle of rational decision making is that of ‘independence
of irrelevant alternatives’. If you prefer a holiday in Mexico to a holiday in
France you should still prefer the Mexican to the French holiday, even
if a third holiday in Canada becomes available. Reason-based decision
making can lead to a violation of this principle. For example, suppose
that you see a popular Canon digital camera for sale at a bargain price
of $200 in a store that is having a one-day sale. You have the choice
between: (a) buying the camera now or (b) waiting until you can learn
more about the cameras that are available. You have no problem in
deciding to buy the camera – you can find a compelling reason to justify
this in the camera’s remarkably low price. Option (a) is clearly preferable
to option (b). However, once inside the store you discover that a Nikon
camera, with more features than the Canon, is also available at a oneoff
bargain price of $350. You now have conflict between the cheaper
Canon and the more expensive, but sophisticated, Nikon. According
to research by Tversky and Shafir, 10 many people would now change
their mind and opt to wait in order to find out more about available
cameras. This is because it is difficult to find a clear reason to justify one
camera’s purchase over the other. The availability of the Nikon camera
has caused you to reverse your original preference of buying the Canon
rather than waiting.
A final interesting consequence of reason-based decision making is
that if an option has some features that are only weakly in its favor,
or irrelevant, this can actually deter people from selecting that option.
For example, in one study, 11 people were asked to choose between two
brands of cake mix which were very similar in all features, except that
the first carried an offer to purchase a collector’s plate which most people
did not want. The offer significantly lowered the tendency to choose the