NASA-TLX

The NASA-TLX (National Aeronautics and Space Administration Task Load Index) is a widely used subjective, multi-dimensional assessment tool that measures perceived workload. It was developed by Sandra Hart and Lowell Staveland at NASA's Ames Research Center in the 1980s.

The NASA-TLX is not a single measure, but rather a weighted combination of six subscales, each representing a different dimension of workload:

• Mental Demand: How much mental and perceptual activity was required (e.g., thinking, deciding, calculating, remembering, looking, searching)? Was the task easy or demanding, simple or complex?
• Physical Demand: How much physical activity was required (e.g., pushing, pulling, turning, controlling, activating)? Was the task easy or demanding, slow or strenuous?
• Temporal Demand: How much time pressure did you feel due to the pace at which the task elements occurred? Was the pace slow and leisurely or rapid and frantic?
• Performance: How successful do you think you were in accomplishing the goals of the task set by the experimenter (or yourself)? How satisfied were you with your performance in accomplishing these goals? Note that higher scores on this scale indicate poorer perceived performance.
• Effort: How hard did you have to work (mentally and physically) to accomplish your level of performance?
• Frustration: How insecure, discouraged, irritated, stressed, and annoyed versus secure, gratified, content, and relaxed did you feel during the task?

The NASA-TLX is administered in two stages. First, participants complete a pairwise comparison of the six subscales, rating which factor was more important to the workload experienced in the task. This process generates weights for each subscale, reflecting its relative contribution to overall workload. Second, participants rate their experience on each of the six subscales using a 20-point bipolar scale (e.g., "Low" to "High").

The weighted workload score is calculated by multiplying the rating for each subscale by its weight and summing the results. The resulting score provides a comprehensive measure of perceived workload, allowing researchers and practitioners to assess and compare workload across different tasks, systems, or conditions.

The NASA-TLX is valued for its sensitivity, diagnostic capability, and relatively simple administration. It has been applied in a wide range of domains, including aviation, healthcare, human-computer interaction, and manufacturing. While other workload measures exist, the NASA-TLX remains a prominent and influential tool in the field of human factors and ergonomics.