Unidimensional versus multidimensional workload scales and the effect of number of rating scale categories

The present study investigated why the Subjective Workload Assessment Technique (SWAT) (a multidimensional scale) has been found to be less sensitive than Overall Workload Scale (OW) (aunidimensional scale) in previous research. It was hypothesized that previous results could be attributed to number of points on the rating scale. To that end, four rating scale groups were employed in which the dimensionality (unidimensional vs multidimensional) and number of rating scale points (7 vs. 19) on the overall workload scale were varied. Forty-eight subjects performed a continuous recognition task composed of 12 levels of difficulty and then rated workload under one of four rating scale conditions (OW-7, OW-19, MOD-SWAT-7, MOD-SWAT-19). Results indicated that: (1) the preponderance of evidence favored equal sensitivity; (2) previous differences between OW and SWAT could not be due to differences in the number of points on the rating scale; and (3) dimensionality affected overall workload ratings in subtle ways. However, the differences found between the unidimensional (OW) and multidimensional (MOD-SWAT) scales is probably attributed to the nature of the task itself where increases in the difficulty in one dimension were accompanied by decreases in another dimension.