SWAT: Do We Need Conjoint Measurement?

Proceedings of the Human Factors and Ergonomics Society Annual

1997

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.

Unidimensional versus Multidimensional Workload Scales and the Effect of Number of Rating Scale Categories

Anthony

Proceedings of the Human Factors and Ergonomics Society Annual

1997

Effect of Pairted Comparison Weighting and Weighting Context

Adams¹,

Proceedings of the Human Factors and Ergonomics Society Annual

2000

The present study compared three subjective workload measurement techniques--a unidimensional scale (UW) and two mutidimenional scales (TLX and ModSWAT)--using a continuous memory task.ModSWAT is a technique that uses the sum of the SWAT dimensions to form the workload composite rather than the standard conjoint measurement procedure. Both weighted and unweighted workload measures were obtained for the two multidimensional scales. The paired-comparison technique used by TLX was employed to weight the three SWAT dimensions. For both multidimensional scales, weighting context was also varied. Paired comparison of the workload dimensions was made either prior to the task in a general context or within context of the task just performed. The major fmdings were that: (I) ModSWAT and UW were more sensitive than TLX to the task demands (i.e., difficulty) of the continuous recognition task; (2) weighting context affected the weights that were assigned the workload dimensions for both TLX and ModSWAT; (3) weighting context did not affect the weighted workload scores; and (4) the weighted and unweighted workload composites were very similar. Results were interpreted within context of averaging across multiple dimensions when several dimensions are insensitive to the task demands. Variability in the weights assigned contributed to the failure to fmd a effect of weighting.

Context Effects in the Measurement of Subjective Workload: Prolonged Exposure to the Same or Different Contexts

Proceedings of the Human Factors and Ergonomics Society Annual

Anthony

2000

The present study investigated the effect of context on the subjective measurement of workload using the continuous memory task. Twelve levels of task difficulty were manipulated either between-subjects or within-subjects. Participants performed the continuous memory task for 48 trials under either a single difficulty level (between-subjects context) or under all 12 difficulty levels (within-subjects context). Workload was measured using ModSWAT— a technique that uses the sum of the SWAT dimensions to form the workload composite rather than the standard conjoint measurement procedure. Results indicated no difference in performance as a function of context but that context affected ratings of subjective workload. Under the single context condition, participants rated the workload of the easiest conditions higher than if the same conditions occurred within context of other more difficult conditions. Results are discussed in terms of their implication for practical assessment of subjective workload.