Older Adult Injury Risk Assessment in the Driving and Occupational Environments

Thesis (Ph.D.)--University of Washington, 2016-08

The United States is experiencing a demographic transition as the population of older adults increases. Many older adults continue to work and drive to support and sustain economic and social health. However, for some, the aging process can be accompanied by declines in cognitive and physical capacity which may increase the risk of a collision or injury. This dissertation examined the association between cognitive and physical function and the risk of motor vehicle collision or occupational injury among older adults. Chapters 2 and 3 explored crash risk associated with cognitive decline and dementia among older drivers. By 2024, 25% of US drivers will be over the age of 65 years. The fatal crash involvement rate among older drivers begins to increase after age 65. Driving simulator and road test studies found lower driving performance associated with lower cognitive function. In chapter 2, we conducted a retrospective cohort study to examine the association between incremental differences in cognition and crash risk among older drivers without dementia. Cognitive function was measured using the Cognitive Abilities Screening Instrument-Item Response Theory (CASI-IRT) score. Older adult participants were drawn from the Group Health Adult Changes in Thought (ACT) Study. ACT records were merged with Washington State crash and licensure records. Eligible participants were age 65 and above and had an active driver's license. We used a generalized estimating equation model with robust standard errors, clustered on the individual. Among ACT study participants, there were 23.4 police-reported crashes per 1000 driver-years. The adjusted incident risk ratio of crash, comparing a higher CASI-IRT score to a score one unit lower was 1.28 (95% CI: 1.08, 1.51). The change in CASI-IRT was not significantly associated with an increase in crash risk. Chapter 3 explored the hazard rate of a crash for older licensed drivers with diagnosed dementia compared to older adults without diagnosis of dementia. This retrospective cohort study used longitudinal clinical and pharmacy records for Group Health members age 65 to 79. Participant records were merged with Washington State police-reported crash records and licensure data from the Washington State Department of Licensing. We assessed the association between diagnosed dementia and crash risk using survival analysis. Dementia was modeled as a time-varying covariate. The overall crash rate was 14.7 per 1,000 driver-years. In a multivariate model, the hazard ratio of crash among those with dementia was 0.56 (95% CI: 0.33, 0.95) relative to older adults without diagnosed dementia. Chapter 4 focused on the association between the physical health of older workers in relation to the job requirements needed for employment and the risk of occupational injury. For this retrospective cohort study, job demands were assessed both objectively (using data derived from an expert panel available through the Occupational Information Network (O*NET)), and subjective assessment of job demand skills as reported by the older worker. Participants were drawn from the Health and Retirement study, a longitudinal national survey composed of biennial interviews age 50 and above. Analyses employed a modified Poisson regression model with robust standard errors, clustered on the individual. Overall, the rate of reporting any injury was 22 per 1000 person-years. Individuals with higher objective or subjective physical job demands were at greater risk of an occupational injury. When physical job demands were high, a mismatch between physical ability and job demands was associated with a two-to-three-fold higher risk of occupational injury.