The NASA Task Load Index (NASA-TLX) is a subjective, multidimensional assessment tool that rates perceived workload, in order to assess a task, system, or team's effectiveness or other aspects of performance. 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.
NASA-TLX originally consisted of two parts: The total workload is divided into six subscales that are represented on a single page, serving as one part of the questionnaire:
- Mental Demand
- Physical Demand
- Temporal Demand
There is a description for each of these subscales that the subject should read before rating. They are rated for each task within a 100-points range with 5-point steps. These ratings are then combined to the task load index. Providing descriptions for each measurement can be found to help participants answer accurately. These descriptions are as follows:
- Mental Demand: How much mental and perceptual activity was required? Was the task easy or demanding, simple or complex?
- Physical Demand: How much physical activity was required? Was the task easy or demanding, slack or strenuous?
- Temporal Demand: How much time pressure did you feel due to the pace at which the tasks or task elements occurred? Was the pace slow or rapid?
- Overall Performance: How successful were you in performing the task? How satisfied were you with your performance?
- Frustration Level: How irritated, stresses, and annoyed versus content, relaxed, and complacent did you feel during the task?
- Effort: How hard did you have to work (mentally and physically) to accomplish your level of performance?
The second part of TLX intends to create an individual weighting of these subscales by letting the subjects compare them pairwise based on their perceived importance. This requires the user to choose which measurement is more relevant to workload. The number of time each is chosen is the weighted score. This is multiplied by the scale score for each dimension and then divided by 15 to get a workload score from 0 to 100, the overall task load index. Many researchers eliminate these pairwise comparisons, though, and refer to the test as “Raw TLX” then. There has been evidence evaluating and supporting this shortened version over the full one since it might increase experimental validity.
The NASA-TLX can be administered using a paper and pencil version, online, or a number of other computerized implementations. 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. While there are multiple ways to administer the NASA-TLX, some may change the results of the test. One study showed that a paper-and-pencil version led to less cognitive workload than processing the information on a computer screen.
- Development of NASA-TLX
- NASA-Task Load Index (NASA-TLX); 20 Years Later
- Task Load Index
- NASA-TLX Task Load Index Website
- Official Website
- NASA (1986). Nasa Task Load Index (TLX) v. 1.0 Manual
- Hart, S., & Staveland, L. (1988). Development of NASA-TLX (Task Load Index): Results of empirical and theoretical research. In P. Hancock & N. Meshkati (Eds.), Human mental workload (pp. 139-183). Amsterdam: North Holland.
- Hart, S. (2006). Nasa-Task Load Index (Nasa-TLX); 20 Years Later. Human Factors and Ergonomics Society Annual Meeting Proceedings, 50, 904-908.
- Schuff, D., Corral, K., Turetken., O. (2011). Comparing the understandability of alternative data warehouse schemas: An empirical study. Decision Support Systems, 52(1), 9-20.
- Rubio, S., Diaz, E., Martin, J., Puente, J. M. (2004). Evaluation of subjective mental workload: A comparison of SWAT, NASA-TLX, and workload profile methods. Applied Psychology: An International Review, 53(1), 63-86.
- Bustamante, E. A., & Spain, R. D. (2008). Measurement Invariance of the NASA TLX. Human Factors and Ergonomics Society Annual Meeting Proceedings, 52, 1522-1526.
- NASA (2003). NASA Task Load Index (TLX): Computerized Version (Version 2.0) [Computer Software]. Moffett Field, CA: NASA-Ames Research Center, Aerospace Human Factors Research Division.
- Noyes, J. M., Bruneau, D. P. J. (2007). A self-analysis of the NASA-TLX workload measure. Ergonomics, 50(4), 514-519.