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The NASA Task Load Index (NASA-TLX) is a subjective, multidimensional assessment tool that rates perceived workload on six different subscales: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration. It was developed by the Human Performance Group at NASA's Ames Research Center over a three year development cycle that included more than 40 laboratory simulations . It has been cited in over 550 studies and a recent search for “NASA-TLX” on Google Scholar revealed over 3,660 articles. These statistics highlight the large influence the NASA-TLX has had in Human Factors research.
The NASA-TLX can be administered using a paper and pencil version or online. If a participant is required to use the TLX tool multiple times, they only need to answer the 15 pairwise comparisons once per task type. If a participant’s workload needs to be measured for intrinsically different tasks, then revisiting the pairwise comparisons may be required. However, according to one school of thought, removing the pairwise comparisons altogether may actually increase experimental validity and reduce experimental error.