Isoperformance: A Methodology for Human Factors Engineering Design

The literature of applied psychology rarely, if ever, allows an unambiguous answer to a particular problem. Almost always there is a hiatus between what is known and what one wants to know. If the tasks are the same, personnel, performance measures, temporal relations or environmental conditions are different. Oftentimes nothing is quite the same as what has been studied in the literature. Inevitably, these gaps are closed by “expert judgment.” People who are experienced in the field extrapolate from what has been studied to the real-world case in hand. This inevitability is not, however, the end of the matter. Expert judgment can be utilized in many different ways and some ways are better than others. The principal issues are: precisely what are the experts to be asked, how is their consensus to be determined, and how is that consensus to be used relative to the real-world problem in hand. This discussion will describe one way of answering these questions. It is called “isoperformance.” The key feature of this approach is the design of an “ideal experiment.” This experiment then functions as a framework for both what is known in the literature and expert judgment.