Thomas Saaty explains how he came up with the 1 to 9 Fundamental Scale of the AHP, the decision-making theory he developed. He observed people could compare two things on a common property, determine which they liked better, and how much better. He created the scale to quantify varying intensities of preference.
The Analytic Hierarchy Process (AHP) is a theory for measuring intangible as well as tangible factors through paired comparisons using judgments from the 1 to 9 Fundamental Scale. Intangibles can have a strong impact in making a decision, and we must first measure them before we can include them as variables. What is most significant is that intangibles can be measured only through the judgments of people and only relative to the goals or concerns of a specific situation. The AHP has been applied in many areas, including resource allocation and conflict resolution.