Workload

Workload is another construct that has no single formal definition, but the gist of it is straightforward. Hart and Staveland (1988) define it as “the cost incurred by a human operator to achieve a particular level of performance.” In other words, it is how “hard” the operator has to work to meet the demands of the task. Often, we are concerned about mental workload in particular. For example, cruising on autopilot should have a low mental workload than, say, landing a helicopter on a ship that is being tossed by waves.

There are several ways to measure workload, which are detailed below:

NASA task load index (TLX). This measure was developed by Hart and Staveland (1988) to include all mental and physical aspects of workload, and it is probably the most popular of workload measures.
Subjective workload assessment technique (SWAT). This measure breaks workload down into three types of load: time, mental effort, and psychological stress. Temporal load is greater when the operator experiences more interruptions, more overlapping events, and less spare time. Mental effort is higher when the task is less automatic, requires more attention, and requires more mental effort. This goes hand-in-hand with the operator’s degree of experience and the complexity of the task. Psychological stress is higher with greater levels of risk, confusion, and frustration, and anxiety (Rubio et al., 2004).
Workload profile (WP). This measure was developed by Tsang and Velazquez (1996) based on Wickens’ multiple resource model of workload. Consequently, it breaks down a task in terms of what modalities are required for its various steps, and so it is easy to point out parts of a task that compete for the same resource. Consider a driver who is attempting to visually attend to both surrounding traffic and navigation instructions on a phone.

Rubio, S., Díaz, E., Martín, J., & Puente, J. M. (2004). Evaluation of subjective mental workload: A comparison of SWAT, NASA‐TLX, and workload profile methods. Applied Psychology, 53(1), 61-86.