21 Analytic hierarchy process
AHP is a multiattribute decision analysis method. Implementation of AHP is useful for complex decisions based on subjective judgments.
AHP is a structured technique for organizing and analyzing complex decisions, based on mathematics and psychology. It was developed by Thomas L. Saaty in the 1970s and has been extensively studied and refined since then. It has particular application in group decision making and is used around the world in a wide variety of decision situations, in fields such as government, business, industry, healthcare, shipbuilding and education. Rather than prescribing a “correct” decision, AHP helps decision makers find one that best suits their goal and their understanding of the problem. It provides a comprehensive and rational framework for structuring a decision problem, for representing and quantifying its elements, for relating those elements to overall goals, and for evaluating alternative solutions. Users decompose their decision problem into a hierarchy of more easily comprehended sub-problems, each of which can be analyzed independently. The elements of the hierarchy can relate to any aspect of the decision problem—tangible or intangible, carefully measured or roughly estimated, well or poorly understood—anything at all that applies to the decision at hand. Once the hierarchy is built, the decision makers systematically evaluate its various elements by comparing them to each other two at a time, with respect to their impact on an element above them in the hierarchy. In making the comparisons, the decision makers can use concrete data about the elements, but they typically use their judgments about the elements’ relative meaning and importance. It is the essence of AHP that human judgments, and not just the underlying information, can be used in performing the evaluations. AHP converts these evaluations to numerical values that can be processed and compared over the entire range of the problem. A numerical weight or priority is derived for each element of the hierarchy, allowing diverse and often incommensurable elements to be compared to one another in a rational and consistent way. This capability distinguishes AHP from other decision making techniques. In the final step of the process, numerical priorities are calculated for each of the decision alternatives. These numbers represent the alternatives’ relative ability to achieve the decision goal, so they allow a straightforward consideration of the various courses of action.
Mechanism
- Identify goal
- Establish criteria affecting goal
- Derive factors affecting each criteria
- Generate alternatives
The above elements each undergo pairwise comparisons.
- 1: elements are equally important
- 3: one element is weakly more important
- 5: one element is strongly more important
- 7: one element is demonstrably important
- 9: one element is absolutely more important
Values of 2,4,6,8 are compromises between the defined categories. Then arrange the values into a matrix.
The pairwise comparison process is inherently subjective. Good experts should be consulted. Ideally, the judgments should be consistent. AHP measures this with the consistency ratio (CR), where CR < 0.100 is acceptable.