Making the case for measuring mental effort

To empirically investigate conceptual modeling languages, subjects are typically confronted with experimental tasks, such as the creation, modification or understanding of conceptual models. Thereby, accuracy, i.e., the amount of correctly performed tasks divided by the number of total tasks, is usually used to assess performance. Even though accuracy is widely adopted, it is connected to two often overlooked problems. First, accuracy is a rather insensitive measure. Second, for tasks of low complexity, the measurement of accuracy may be distorted by peculiarities of the human mind. In order to tackle these problems, we propose to additionally assess the subject's mental effort, i.e., the mental resources required to perform a task. In particular, we show how aforementioned problems connected to accuracy can be resolved, that mental effort is a valid measure of performance and how mental effort can easily be assessed in empirical research.