NASA-TLX (Wikipedia)
An encyclopedia article on the NASA Task Load Index (NASA-TLX): a subjective, multidimensional workload-rating questionnaire developed by NASA Ames Research Center’s Human Performance Group. Wikipedia articles are continuously edited, so year above reflects the access date, not a fixed publication year.
License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/
Key points
- Each of the six subscales (Mental Demand, Physical Demand, Temporal Demand, Own Performance, Effort, Frustration Level) is rated on a 100-point scale in 5-point steps, using a fixed descriptive question for each (e.g. Mental Demand: “How much mental and perceptual activity was required? Was the task easy or demanding, simple or complex?”).
- Full scoring has two parts: six subscale ratings, plus a one-time-per-task-type pairwise-comparison step where the participant picks, across all 15 possible pairs of the six subscales, which felt more relevant to the workload experienced; each subscale’s win count becomes its weight. The overall 0–100 score is the sum of (rating × weight) divided by 15.
- “Raw TLX,” a widely-used simplification, skips the pairwise-weighting step and simply averages the six subscale ratings — evidence suggests this can even increase experimental validity by removing an extra, error-prone judgment task — and allows an irrelevant subscale to be dropped for a specific task.
- If a participant repeats the questionnaire for the same task type, only the six subscale ratings need to be redone each time; the pairwise weighting is reused unless the task itself changes in kind.
- Administration format isn’t neutral: one study found a paper-and-pencil version produced lower measured workload than the identical content presented on a computer screen, though other computer- and wearable-based versions still reliably track relative workload changes. The Official NASA TLX iOS app uses a continuous “Subjective Analogue Equivalent Rating” slider built to reproduce the paper form’s unanchored feel, unlike unofficial computerized versions that use a discrete, locking scale.
- Developed over a three-year cycle including more than 40 laboratory simulations; cited in over 4,400 studies across aviation, healthcare, and other complex socio-technical domains.