Introduction to the special section: Can workload take the strain?

This issue of the journal includes a special section examining the concept of workload. We hope that this will be the first in an occasional series that examines some of the fundamental concepts used in discourse about human interaction with technology and organisations. The discussion was sparked by the paper by de Winter which challenges the human factors community to be more reflective about the use of various constructs and about workload in particular. Given the importance of the topic, we invited a number of commentaries from recognised experts in the area, hence the contributions from Annie Pauzié, Dick de Waard and Ben Lewis-Evans, and Armin Eichinger and Klaus Bengler. The debate is framed around such fundamental questions as whether the concept of workload is scientifically valid, whether even though it may not have full scientific validity it is useful, and whether if it is useful we have appropriate and reliable measurement tools. The concept of workload is a slippery one. Definitions vary quite considerably. Eggemeier and O’Donnell (1982) state: ‘‘Mental workload is the term which has been used in referring to the degree or percentage of the operator’s information processing capacity which is expended in meeting system demands’’. This is very similar to the definition provided by de Waard and Lewis-Evans in this issue: ‘‘Two factors always play a role, on the one hand the properties of the (mental or physical) task at hand, which we will refer to as the task demands, on the other hand the capability of the operator to perform the task, referred to as capacity. Workload in our view is the interaction between these two, in other words, the proportion of capacity that is used to perform a task’’. But other definitions are far broader. Meshkati (1988) defined workload as a construct of a variety of components: ‘‘There are numerous theories attempting to define mental workload and its major components, and to demonstrate the existing interrelationships.... These models generally consider mental workload as a multi-dimensional construct that reflects the interaction of such elements as task and system demands, operator processing capabilities and effort, subjective performance criteria, operator information processing behavior and strategies, and finally operator training and prior experience’’. This leads to the issue of measurement. If workload is a construct, how do we measure it? Even if we have a quasimathematical definition of it in terms of the proportion of capacity that is used to perform a task, how do we measure numerator and denominator? Since it is not possible to identify someone’s total information processing capacity, how can we realistically measure the proportion currently being expended? De Waard and Lewis-Evans acknowledge the difficulty of measuring workload representationally, i.e. by scientific mathematical measurement. But as de Winter points out, in many areas of psychology and human factors, we are perfectly content to measure fuzzy concepts such as intelligence, quality of life or acceptance by operationalised subjective means. However, we must be cautious about how we use the values obtained: the ratings of workload have no absolute value and, as pointed out by de Waard and Lewis-Evans, should properly only be compared between different conditions in within-subjects designs. Of course, we could turn to ‘‘objective’’ physiological measure of workload and thus eliminate all the problems and difficulties associated with using subjective assessment O. Carsten (&) Institute for Transport Studies, University of Leeds, Leeds LS2 9JT, UK e-mail: O.M.J.Carsten@its.leeds.ac.uk