NASA Task Load Index
Separate dimensions of perceived workload
NASA-TLX measures subjective workload through mental demand, physical demand, temporal demand, performance, effort and frustration ratings. The original procedure weights dimensions through paired comparisons; raw TLX uses an unweighted aggregation. These variants must be named and scored consistently. Workload ratings complement performance measures because effort, success and interface usability are different constructs.
Use it when task demands or workload trade-offs matter, such as interface changes, multitasking or training, and participants can give ratings after a clearly defined task or episode.
Strengths
- Distinguishes several contributors to perceived workload
- Can reveal burdens hidden by unchanged task accuracy
Limitations
- Subjective ratings depend on context and comparison standards
- Changing items or weights undermines comparability
Know the boundary
A lower workload rating is not automatically better if it reflects disengagement, underload or reduced task demands.