The rational model and disjointed incrementalism represent opposite poles. Various intermediate approaches have also been proposed, perhaps the best known of which is "mixed scanning" by sociologist Amitai Etzioni.9
The idea is quite simple. Etzioni advocates a two-step process. First, a general scanning process is conducted to get the overall picture and to decide which elements merit more detailed examination. Etzioni uses the analogy of a weather monitoring system utilizing space satellites.
The rationalistic approach [rational model] would seek an exhaustive survey of weather conditions ... by scheduling reviews of the entire sky as often as possible. This would yield an avalanche of details, costly to analyze and likely to overwhelm our action capabilities.
He then goes on to contrast the rational model approach with his mixed scanning approach.
A mixed scanning strategy would include elements of both approaches ... a broad angle camera that would cover all parts of the sky but not in great detail and a second one which would zero in on those areas revealed by the first camera to require more examination. While mixed scanning might miss areas in which a detailed camera could reveal trouble, it is less likely than incrementalism to miss obvious trouble spots in unfamiliar areas.
Etzioni elaborates on his model by pointing out that the scanning process might actually have more than one stage. We might scan a large field quickly and then, depending on what we had learned, scan a smaller field somewhat more thoroughly. When we have located the area that deserves fine scrutiny, a systematic approach such as that of the rational model is appropriate.
Etzioni argues that his model avoids the excessive commitment to precedent and past experience inherent in the incremental model. At the same time, it is far more feasible than a doctrinaire rational model approach: "The strategy [mixed scanning] combines a detailed ('rationalistic') examination of some sectors—which, unlike the detailed examination of the entire area, is feasible—with a 'truncated' review of other sectors." Etzioni's advice resembles that given to strategic planners, sometimes summarized under the acronym SWOT, which stands for Strengths, Weaknesses, Opportunities, Threats. The advice is quickly to characterize the organization's overall position under those four general categories. When that general reconnaissance is done, then detailed planning following a structured, rational model-like approach can begin, with less fear of being blindsided by important factors that were overlooked in a rush to premature closure.
Mixed scanning has generally received a favorable response from planners interested in how-to-plan or what-is-planning questions. It seems to describe a fair amount of what planners actually do. The working planner is likely to spend a little time looking around very broadly, narrow his or her options quickly, and focus intently on a small range of possibilities. Etzioni's synthesis appears to allow the user the strengths of both models while minimizing their weaknesses.