Comparison of Four Subjective Workload Rating Scales

Four subjective workload scales were compared along four dimensions: sensitivity, operator acceptance, resource requirements, and special procedures. The scales were the Modified Cooper-Harper scale, the National Aeronautics and Space Administration Task Load Index (TLX), the Overall Workload (OW) scale, and the Subjective Workload Assessment Technique. Three U.S. Army systems were studied for potential workload concerns. Data from five different studies on the three systems were compared along the aforementioned four dimensions. Results indicate that all four scales are acceptable tools and are sensitive to different levels of workload. However, TLX and OW are consistently superior when considering sensitivity, as measured by factor validity, and operator acceptance. This research is an example of a systematic approach for examining human factors measurement tools.