FIGURE B-1 Stacey Diagram: Zone of complexity. SOURCE: Stacey, 1996.

For other issues in human systems for which there is very little certainty and very little agreement (the area in the upper right of Figure B-1), chaos reigns and is to be avoided. A riot in the streets is an example.

Mechanical systems thinking (as intuitively applied by people designing and managing organizational systems) seems to allow only these two possibilities; it is necessary to plan and control, or there will be chaos. This seems so obvious to our mechanical-thinking mental model that it may not always be consciously acknowledged. Complex adaptive systems thinking allows for a third possibility.

There are many issues in human systems that lie in a “zone of complexity” (Langton, 1989; Zimmerman et al., 1998). These are issues for which there are only modest levels of certainty and agreement. Examples of such issues in health care might include: How should health care be financed? What is the best way to deliver primary care? For such issues there are many different models that have been successful in some situations and less successful in others; that is, only a modest level of “certainty” exists regarding what actions lead to what outcomes. Further, well-meaning, rational, intelligent people might not always agree as to the approach or outcome, meaning that there are only modest levels of agreement. For the most part the issues associated with designing the 21st-century health care system are in the zone of complexity where it would be more appropriate to use the paradigm of a complex adaptive system.


A complex adaptive system (CAS) is a collection of individual agents that have the freedom to act in ways that are not always predictable and whose actions

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