People face making decisions both in their professional and private lives. A manager
in a company, for example, may need to evaluate suppliers and develop partnerships
with the best ones. A household may need to choose an energy supplier for their
family home. Students cannot ignore university rankings. Often candidates for a job
vacancy are ‘ranked’ based on their experience, performance during the interview,
As well as ranking and choice problems, there are also classification problems
that have existed since classical times. In the fourth century bc, the ancient Greek
philosopher Epicurus arranged human desires into two classes: vain desires (e.g.
the desire for immortality) and natural desires (e.g. the desire for pleasure). These
classifications were supposed to help in finding inner peace. Nowadays, classification
problems occur naturally in daily life. A doctor, for instance, diagnoses a patient
on the basis of their symptoms and assigns them to a pathology class to be able
to prescribe the appropriate treatment. In enterprise, projects are often sorted into
priority-based categories. Not long ago, a study showed that over 20 million Brazilians
have moved from the lower social categories (D and E) to category C, the first
tier of the middle class, and are now active consumers due to an increase in legal
employment (Observador 2008). Hurricanes or cyclones are sorted into one of the
five Saffir–Simpson categories based on their wind speed, superficial pressure and
All of these examples show that delicate decision problems arise frequently.
Decision problems such as ranking, choice and sorting problems are often complex as
they usually involve several criteria. People no longer consider only one criterion (e.g.
price) when making a decision. To build long-term relationships, make sustainable
and environmentally friendly decisions, companies consider multiple criteria in their