Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED105- AC/243(Panel-8)TR/7Volume 25.5 SUBJECTIVE WORKLOAD ASSESSMENT TECHNIQUE (SWAT)What the technique doesprovides a measure of subjective workload. Workload is defined as composed of three orthogonal dimensions: timeload, mental effort load, and psychological stress load. Each dimension is represented in SWAT by a three-pointrating scale with verbal descriptors. In the first phase, the scale is developed for the application and user population ofinteresL Individual assessments are scaled, and conjoint analysis (Reid & Nygren, 1988) is carried out an the results,to convert them into a single metric of workload. If the data have a limited number of ordinal-scale features, then theconjoint scaling can develop an interval scale from the data.In the application phase, the basic SWAT scales are used, and the results converted to a single workload scale usingthe results of the conjoint scaling. Although the technique was intended for use in the evaluation of workload inactual systems, or in man-in-the-loop simulations. it can be applied by experts at the drawing-board level, to predictoperator workload prior to a system being built (Kupcrman. 1985). In such applications it is referred to as Pro-SWAT(Projective SWAT).TIME LOADTable 5.5: SWAT dimensions1. Often have spare time: interruptions or overlap among activities occur infrequently. if at all.2. Occasionally have spare time: interruptions or overlap among activities occur frequently.3. Almost never have spare time: interruptions or overlap among activities are very frequent or occur all the time.MENTAL EFFORT LOAD1. Very little conscious mental effort or concentration required: activity is almost automatic. requiring little or no attention.2. Moderate conscious mental effort of concentration required: complexity of activity is moderately high due to uncertainty,unpredictability, or unfamiliarity: considerable attention required.3. Extensive mental effort and concentration are necessary: very complex activity requiring total attention.PSYCHOLOGICAL STRESS LOAD1. Little confusion, risk, frustration, or anxiety exists and can be easily accommodated.2. Moderate stress due to confusion, frustration. or anxiety noticeably adds to workload: significant compensation is/required to maintain adequate performance.3. High to very intense stress due to confusion, frustration. or anxiety: high to extreme determination and self-controlrequired.NATO UNCLASSIFIED- 105 -