Multi-Criteria Decision-Making

Multi-Criteria Decision-Making (MCDM) is a way of choosing systematically between multiple options. It’s fast and simple, but needs to be used with caution, because it can produce a misleading impression of objectivity.

The core of MCDM is a table of options and attributes. Each option gets a column; each attribute gets a row. You then score each option against each attribute to get the value for each cell, as shown below.

In the image opposite, for an unweighted MCDM table, the values are on a scale from 1 to 7, with 7 being the most desirable. All of the attributes are treated as equally important. The option with the highest total score is B, with a score of 15.

Often, some attributes are more important than others. You can take account of this by multiplying the more important attributes by a weighting factor, as shown in the weighted MCDM table opposite. In this table, size is twice as important as speed, so the original values for size are multiplied by 2. Cost is three times as important as speed, so the original values for cost are multiplied by 3. With these new values,  the highest score is now for option F.

The weighting system is open to obvious abuse, as is the choice of attributes. It’s easy for users with vested interests to choose weightings and attributes that produce the outcome they want.

This risk can be reduced by having a clear process showing how you identified the key attributes and the weightings during a systematic elicitation process.