Analysis Techniques For Man-Machine Systems Design

fl1106AC/243(Panel 8'TR/7- 106Volume 2N A T OU N CL A SSI FI EDInputs to the techniqueOutputs of the techniqueUsers need to be practised in using the technique, and to The scaled outputs from user ratings show workload onhave ranked all combinations of the time-load, mental- an interval scale of "workload units." between I and 100.load, and stress (27 combinations). Once the rank-orderof the 27 combinations has been determined by theindividual, the technique can be applied. For Pro-SWATapplications, the user requires a full understanding of thetime-scale and sequence of events, and familiarity withthe proposed human-machine interface.When to usePro-SWAT can be applied in the concept development or design definition phase, once details of the h4g~man-machineinterface are available. Man-in-the-loop applications of SWAT require a simulation, and are best suited to the latter.stages of design definition, or to Test and Evaluation (Acton & Rokicki, 1986).vRelated techniquesSWAT belongs to the family of subjective workload assessment methods, but is distinct in the use of threedimensions and conjoint measurement.Resources requiredThe technique requires a set of 27 cards, for each combination of ratings, and the SWAT software.AdvantagesSWAT is straightforward to use, and can easily beapplied to many tasks.DisadvantagesThe technique requires a significant administrauvecommitment, to develop the scales for the potential raters,compare scales across raters, train raters in the applicationof the technique, and perform the scaling. The output scaleof "workload units" does not include criteria foracceptability or for rejection. Therefore, the technique isbest used to compare competing designs rather thandeveloping one preferred design. In practice, the use ofSWAT for man-in-the-loop applications is sometimesinvasive.Reports of Pro-SWAT applications are convincing, but thetechnique has not been validated thoroughly in suchapplications. The technique cannot be applied until detailsof the human-machine interface are available.NATOUNCLASSIFIED- 106 -