A Hierarchy of Objectives

Objectives tend to occur in hierarchies. The most general objective, in order to be realized, will have several sub-objectives that first must be successfully accomplished. Each of those sub-objectives can also have sub-objectives, and so on, in a hierarchy that can consist of several layers of objectives.

For example, suppose that our general objective (goal) is to reduce the losses caused by potato late blight in a particular field. We could construct a hierarchy of objectives as follows:

First-level objective (Goal): Reduce the losses caused by potato late blight

Second-level objective: Reduce the level of foliage infection

Second-level objective: Reduce the level of tuber infection

Note that this is just a slice out of a much larger hierarchy of objectives. What we, as plant pathologists or pest control specialists, might set as our most general objective would simply be an intermediary objective for a grower, who has to manage other pests, manage the crop, and be concerned with the productivity of the whole farm. At the other end of the scale, under some of our fourth-level objectives we could create a fifth level and perhaps even a sixth. For example, "Apply fungicides as necessary" would require some determination of the susceptibility of the variety that we had planted, an assessment of the inoculum available, and an assessment of the environmental conditions, perhaps requiring the use of a predictive model.

Note also that there are many valid ways to structure a hierarchy of objectives to accomplish a given goal, even starting with the same lowest-level objectives. The nature of the plan for organizing the objectives depends on the biases of the planner, and while some plans may be better than others for accomplishing the goal, the others are not necessarily wrong.

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