Session instrument
NASA Task Load Index
NASA-TLX
Measures: Perceived load, separated into six sources
It answers “which of the two versions weighs more?” with a defensible number, and — what matters more — says what the load is made of. Two screens can tie on the overall score for opposite reasons, and the fix for each is different.
The world’s most widely used instrument for measuring perceived workload was created by NASA to assess aircraft cockpits and has reached us practically unchanged (HartCreated the NASA-TLX, the workload questionnaire that was born in an aircraft cockpit and remains in use almost unchanged.One reference in this work:1988Development of NASA-TLX (Task Load Index): results of empirical and theoretical researchSee in the bibliography → and Staveland, 1988). What makes it useful in design is the separation: instead of asking “was it hard?”, it breaks difficulty down into six sources, and it is the breakdown that gives the diagnosis. A screen heavy on mental demand calls for less simultaneous information; one heavy on frustration calls for something else entirely, and the overall score does not distinguish the two. It is the accessible counterpart of EEG: it measures the same phenomenon that cognitive load theory describes, but through the door of self-report.
How to run itAt the end of each task, six scales from 0 to 100: mental demand, physical demand, temporal demand, performance, effort and frustration. Five minutes per participant, on paper or in a form.
SeesComparable across versions, with decades of reference data and a cost close to zero.
Does not seeIt is self-report after the fact: it measures the impression that remained, not the effort in the moment.