Pre- and post-DSSQ responses were therefore used to compute pre-post z scores for the three DSSQ factors.
Inspection of the DSSQ and OPI scores of these two individuals indicated that they did not differ from their group mean (the false alarm-KR condition) on the OPI or DSSQ scales by more than 1.5 standard deviations.
Accordingly, together with assessing the effects of the sensory modality of signals on perceived mental workload, the present study also sought to determine the multidimensionality of sensory-determined stress in sustained attention by means of the DSSQ. Finally, the present study was also designed to examine the manner in which self-reports of stress might change over time.
Perceived stress was measured using the DSSQ administered in two parts: a previgil questionnaire, completed prior to the initiation of the vigil, and a postvigil questionnaire, completed after the vigil.
Following the instructions, half the participants completed the previgil version of the DSSQ and then engaged in a 5-min practice session with the sensory modality they would later encounter in the main portion of the session.
All pre- and postvigil comparisons on the DSSQ were made in terms of standard scores (z scores) using the formula (phase score--normative mean)/standard deviation of the normative sample.
Within the standard and modified groups, 16 monitors (8 women, 8 men) were selected at random to complete the NASA-TLX, and the remainder completed the DSSQ. This procedure was employed to minimize possible interscale interactions.
The remainder completed the pre- and posttask versions of the DSSQ. The card-sort task was included to ensure that the absence of workload and/or stress differences between the two vigilance conditions could not be attributed to a lack of sensitivity on the part of the NASA-TLX or the DSSQ.
The 10 DSSQ scale scores were standardized against normative data secured from a large British sample (Matthews et al., 1999), using the formula (raw score--norm group factor mean)/ norm group factor standard deviation.
Validity of the DSSQ scales is also supported by evidence that scores are systematically related to participants' appraisal of the task as threatening or challenging as well as their choice of coping strategies (Matthews et al., 1999).
Pre- and posttask versions of the DSSQ have also been developed.
Initial analysis of the DSSQ data showed that (a) there were no significant differences in pretask scores between the easy and difficult conditions and (b) means and standard deviations for pretask scores were similar to normative values reported by Matthews et al.