Weighted product model

The weighted product model (WPM) is a popular multi-criteria decision analysis (MCDA) / multi-criteria decision making (MCDM) method. It is similar to the weighted sum model (WSM). The main difference is that instead of addition in the main mathematical operation now there is multiplication. As with all MCDA / MCDM methods, given is a finite set of decision alternatives described in terms of a number of decision criteria. Each decision alternative is compared with the others by multiplying a number of ratios, one for each decision criterion. Each ratio is raised to the power equivalent to the relative weight of the corresponding criterion. Some of the first references to this method are due to Bridgman and Miller and Starr.

More details on this method are given in the MCDM book by Triantaphyllou.

Suppose that a given MCDA problem is defined on m alternatives and n decision criteria. Furthermore, let us assume that all the criteria are benefit criteria, that is, the higher the values are, the better it is. Next suppose that w_j denotes the relative weight of importance of the criterion C_j and a_ij is the performance value of alternative A_i when it is evaluated in terms of criterion C_j. Then, if one wishes to compare the two alternatives A_K and A_L (where m ≥ K, L ≥ 1) then, the following product has to be calculated:

If the ratio P(A_K/A_L) is greater than or equal to the value 1, then it indicates that alternative A_K is more desirable than alternative A_L (in the maximization case). If we are interested in determining the best alternative, then the best alternative is the one that is better than or at least equal to all other alternatives.

The WPM is often called dimensionless analysis because its mathematical structure eliminates any units of measure.

Therefore, the WPM can be used in single- and multi-dimensional MCDA / MCDM problems. That is, on decision problems where the alternatives are described in terms that use different units of measurement. An advantage of this method is that instead of the actual values it can use relative ones.

The following is a simple numerical example which illustrates how the calculations for this method can be carried out. As data we use the same numerical values as in the numerical example described for the weighted sum model. These numerical data are repeated next for easier reference.

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