Development of a theoretical framework and design tool for process usability assessment

The purpose of this research was the development and validation of a hybrid theoretical model of usability and the translation of this model into a functional software tool which can immediately aid industry in improving system design. A host of studies can be found for developing the static elements of the human-machine interface, such as keyboard design, workstation layout and graphical displays, but very little is available to help the engineer design the interaction process. The process, as defined here, is the sequence of decisions and actions users go through to complete a task using the machine or technology. Present research in evaluating these interaction process features is such that application of these techniques to engineering design is not straightforward, requires highly skilled personnel and is quite time-consuming. The theory base for this research combines several theoretical views of the interaction process into a hybrid model which accounts for a greater degree of variance in usability than each view alone. Upon the basis of this hybrid model, a software tool was produced which engineers can use to model their process or procedure design. The feedback provided by this tool can then be used by the designer to improve the interaction process. This technique was validated in both the laboratory and the field. Sixty people were asked to perform thirty tasks using a prototype vending machine. Their perceived usability, errors, mental effort, and time to completion were recorded and compared to predictions made by the software tool. The tool was able to predict perceived usability, mental effort, and time to completion with significant accuracy. In the field validation, 100 observations were made of customers using the same vending machine. The time to task completion and perceived satisfaction with the system were recorded and compared to predictions made by the software tool. Again, the tool was able to make statistically significant predictions. Results of the validation of this technique indicate that the hybrid model produces predictions of aspects of task performance and that the technique transfers from the laboratory to the real world