Phase 3: Strategies Analysis
Heuristic strategies can be highly accurate in some environments, but no single heuristic does well across all contexts. This suggests that if a decision maker wanted to achieve both a reasonably high level of accuracy and low effort, he or she should have to use a repertoire of strategies, with selection contingent upon situational demands. -- J. W. Payne et. al. ( 1993, p. 131)
To support system design we do not need detailed process models of the mental activities which are used by the operators. System design must be based upon higher level models of the structures of effective mental processes which the operators can be used and their characteristics with respect to human limitations and preferences so that operators can adapt individually and develop effective strategies. Rather than descriptions of the course and content of actual mental processes, we need descriptions of the structures of possible and effective mental processes. -- Rasmussen ( 1981, p. 242)
Our objective in this chapter is to describe the third phase of CWA, strategies analysis, in full detail. As we discussed in chapter 5, the value added by strategies analysis lies in understanding the different ways of accomplishing the activities identified in a control task analysis. Thus, whereas the previous chapter dealt with the question of what needs to be done, this chapter deals with the question of how it can be done. We describe information flows maps ( Rasmussen, 1980, 1981) as a modeling tool that can be used to conduct such an analysis. A detailed example of the strategies analysis is then presented for the DURESS II process control microworld. By the end of this chapter, you should understand how strategy constraints inherit, and built on, the work domain and control task constraints discussed in the previous two chapters.
We begin by showing the relationship between strategies analysis and control task analysis. Then, we use an example from air traffic control to show why workers often switch between several strategies to cope with task demands. This intuition- building example is followed by a generic definition of the term strategy. This definition helps to illustrate the importance of strategies analysis in CWA.