Relationship of Driving Comfort to Perceived and Objective Driving Abilities and Future Driving Behaviour
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Introduction: Bandura’s self-efficacy theory postulates that confidence is a stronger determinant of behaviour than one’s actual skills or abilities. The Day and Night time Driving Comfort Scales (D-DCS and N-DCS) are new tools to measure perceived confidence in older drivers. Developed inductively with older drivers, the DCSs have good structural properties and preliminary psychometric support, including test-retest reliability. Purpose: This thesis builds on previous work by further examining the construct validity of the DCSs via (1) temporal associations (Study 1) and (2) cross-sectional relationships (Study 2). Study 1 prospectively examined the relationship between DCS scores and self-reported driving behaviour. Study 2, meanwhile, examined cross-sectional associations between DCS scores and selected sample characteristics, self-reported driving behaviour and driving problems, perceived abilities and seven objectively measured driving-related abilities (visual acuity, contrast sensitivity, disability glare, brake reaction time, lower body mobility, executive skills and visual attention). Methods: For Study 1, a convenience sample of 82 older drivers (aged 63 to 93) were assessed at baseline and follow-up (five to 17 months later). Study tools comprised the DCSs, multi-item ratings of driving frequency, avoidance and perceived abilities and a background questionnaire. Telephone interviews were conducted with a subgroup of 45 drivers to examine reasons for changes in driving comfort. For Study 2, cross-sectional relationships with the DCSs were examined using baseline data from 65 drivers (aged 63 to 93). A subgroup of 42 participants completed objective assessments of driving-related abilities assessed via ETDRS charts, Pelli-Robson charts, Brightness Acuity Tester, brake reaction time apparatus, the Rapid Paced Walk, the Trail Making Tests (Parts A and B) and the UFOV subtest 2. Results: Prospectively, lower baseline N-DCS scores (p<.001) and decreased N-DCS scores (p<.001) were significant predictors of lower self-reported situational driving frequency (R2 = 34%) and greater situational avoidance (R2 = 51%) at follow-up. While DCS scores did not change appreciably for those who continued driving, N-DCS scores were significantly lower at follow-up for seven individuals who stopped driving (p<.05). Cross-sectionally, lower DCS scores were significantly associated with lower self-reported situational driving frequency, higher situational avoidance and lower ratings of perceived abilities (p<.001). Poorer left eye acuity scores were significantly associated with lower D-DCS (p<.05) and N-DCS (p<.05), while slower performance on Part A of the Trail Making Test was significantly related to lower D-DCS scores (p<.05). Participants with a discrepancy between their perceived and actual abilities had significantly higher D-DCS, situational driving frequency and lower situational avoidance (p<.05). Conclusions: Findings are consistent with Bandura’s self-efficacy theory and Rudman’s model of driving self-regulation and, thus, provide further support for the construct validity of the DCSs. Further studies are needed with larger, more diverse samples, including those with diagnosed impairments, to establish benchmarks for driving comfort in healthy drivers and various clinical populations (such as those with stroke, Parkinson’s or visual conditions). Prospective studies should also involve longer follow-up periods, examination of actual driving behaviour and barriers to self-restriction, and attempt to pinpoint whether there is a critical level of discomfort at which voluntary cessation is likely to occur.