The NASA Task Load Index (NASA-TLX) is a subjective, multidimensional workload assessment tool. It was developed by the Human Performance Group at NASA Ames Research Center over a three year development cycle that included more than 40 laboratory simulations. It is thought to be one of the most validated workload measurement tools in Human Factors Psychology and Engineering.
The NASA-TLX rates perceived workload on six different scales: Mental Demand, Physical Demand, Temporal Demand, Performance, Effort, and Frustration. According to Hart and Staveland (1988), a participant should first rate the six scales according to how much they contributed to the workload required for the task being studied. After the ratings, each of the six scales is weighted. The weightings are achieved by answering 15 pair-wise comparisons and are designed to greatly enhance the sensitivity of the overall workload score while reducing between-rater variability.
The pair-wise comparisons component is only needed after each distinctly different task. When completing similar tasks, it was found that the comparisons did not significantly add to the overall sensitivity of the tool. Some schools of thought go as far as to suggest that the pair-wise comparisons are never needed. This tool let’s you select the method that best suits your preferences.