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1 Birmingham/Atlanta Geriatric Research Education and Clinical Center (GRECC), Alabama.
2 Birmingham VA Medical Center, Alabama.
3 Center for Aging and the Division of Gerontology, Geriatrics, and Palliative Care, University of Alabama at Birmingham.
Address correspondence to Richard V. Sims, MD, Birmingham/Atlanta GRECC, Room 8B-8213, 700 19th Street South, Birmingham, AL 35233. E-mail: richard.sims{at}med.va.gov
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Methods. Data on SRH (poor, fair, good, very good, or excellent), medical diagnoses, physical performance, visual acuity, driving status, and other relevant covariates were collected from 649 community-dwelling older Alabama drivers during in-home interviews. Using multivariable logistic regression analyses, we estimated the association of SRH with driving cessation 2 years later.
Results. Participants had a mean age of 74 years; 43% were women, 41% African American, and 48% rural. Overall, 36% reported poor to fair SRH at baseline, and 11% had stopped driving after 2 years. Compared to 8% of drivers with good to excellent SRH, 17% with poor to fair health stopped driving (adjusted odds ratio [OR], 1.93; 95% confidence interval [CI], 1.09–3.41; p =.025). Lower Short Physical Performance Battery (SPPB) scores (adjusted OR, 0.86; 95% CI, 0.78–0.95; p =.001) and older age (adjusted OR, 1.06 per year; 95% CI, 1.01–1.11; p =.010) were also associated with driving cessation. Receiver operating characteristics curves documented similar predictive discrimination (c statistics) for SRH (0.72), the SPPB (0.70), and a count of comorbidities based on the Charlson Comorbidity Index (0.73).
Conclusions. Poor to fair SRH predicted incident driving cessation after 2 years in a cohort of older adults. SRH can be easily obtained during clinic visits to identify at-risk drivers.
Dellinger and colleagues suggest that a general measure of health and functional status is needed to elucidate the relationship between medical conditions and driving for older adults (11). Self-reported health (SRH) is perhaps such a measure. Studies have noted that SRH predicts mortality among older individuals. The personal perception of one's health may indicate an awareness of prior and current health experiences, lifestyle choices, as well as comparisons with persons of similar age, gender, and race (12,13). Whether SRH is associated with other outcomes, such as mobility, is controversial. In one study, older former drivers described their health as good or very good, whereas in another, higher values on a "health perceptions index" were associated with continued driving after age 50 years (7,11). Anstey and coworkers (14) recently reported that poor SRH independently predicted driving cessation in a prospective cohort study of Australian drivers who were 70 years old or older.
The purpose of this study was to test the hypothesis that SRH predicted driving cessation in a cohort of community-dwelling African American and white Alabama drivers, who were at least 65 years old at baseline. A secondary objective of our study was to compare the predictive validity of SRH with a measure of physical function, the Short Physical Performance Battery (SPPB), and the Charlson Comorbidity Index (CCI), respectively, on driving cessation. We hypothesized that poor to fair health would be associated with incident driving cessation and would be as effective as the SPPB and the CCI for predicting this outcome.
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Predictor Variable
SRH was the primary predictor variable. Participants were asked "In general, how would you say your health is: poor, fair, good, very good, or excellent?"
Outcome Variable
A telephone interview 2 years after the baseline visits included the following question about driving status: "Tell me which one of the following statements best describes your driving: You have never driven, you do not drive now, you drive only short distances, or you drive anywhere you want." Persons who previously reported driving and who indicated that they did not drive now were considered to have experienced incident driving cessation in the prior 2 years.
Covariates
Information collected at baseline included sociodemographic factors, verified medical diagnoses, and information on medications, and geriatric syndromes. Participants showed the interviewer all medications they were taking. Geriatric syndromes were defined by their predilection for older adults and their multifactorial pathogenesis. Geriatric syndromes considered in this study included falling, urinary incontinence, unexplained weight loss, and dizziness. All participants completed the Mini-Mental State Examination (MMSE), the 15-item Geriatric Depression Scale (GDS), and visual acuity testing with Snellen eye charts (16).
CCI.-- Charlson and colleagues (17) created a measure predictive of 1-year survival for inpatients, based on the sum of comorbid illnesses adjusted for their relative weights. A modified index was created by summing the verified diagnoses of diseases without consideration of the severity or weighing of the individual conditions with higher scores indicating a greater burden of overall comorbidity. A disease or condition was considered verified if the participant reported taking a medication for the condition, if their primary physician reported that he or she had the condition, or if the condition was documented on a hospital discharge form within the 3 years before entry into the study.
SPPB.-- Developed by Guralnik and colleagues (18), the SPPB includes timed tests of balance, walking speed, and successive chair stands. A score was calculated, based on the sum of the highest quartiles achieved (i.e., 0 = unable to do and 4 = the highest quartile) for each of the three tasks. Thus, individuals in the highest quartile for all three tasks would have an SPPB score of 12.
Statistical Analysis
For the descriptive analyses, participants were categorized by health status into two groups: poor to fair SRH and good to excellent SRH. Chi-square tests and Mann–Whitney U tests were used as appropriate to compare baseline characteristics between participants in the two categories. The proportion of former drivers in each of the five health categories (i.e., poor, fair, good, very good, and excellent) was tested for significance using chi-square tests. To determine the independence of the association between SRH and driving cessation, a multivariable logistic regression model was constructed in which poor to fair SRH served as the independent variable, with driving cessation at 2 years acting as the dependent variable. Covariates included age, gender, education, race, visual acuity, and MMSE, GDS, CCI, and SPPB scores.
To compare the ability of SRH and scores on the SPPB and CCI to predict driving cessation, bivariate logistic regression models estimated their probabilities of predicting driving cessation. We then constructed receiver operating characteristic (ROC) curves for the three predictor variables, using driving cessation at 2 years as the test variable. The c statistic test was used to test their discriminating abilities.
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Comparative Discrimination of SRH, SPPB, and CCI
Overlapping areas under the curve (AUCs) for predicting driving cessation were shown for ROC curves for SPPB (.682; 95% CI,.614–.750) and CCI scores (.714; 95% CI,.653–.775), and for SRH (.700; 95% CI,.636–.763) (Figure 2).
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DISCUSSION |
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Consistent with other studies (12,13), the SRH variable appeared to be a valid measure of overall health status. We noted that seniors with worse SRH had higher rates of specific medical diagnoses, geriatric syndromes, overall comorbidity, and poorer performance on tests of vision, cognition, affect, and physical performance. In a secondary analysis of the Canadian Study of Health and Aging, Walker and colleagues (13) noted that poor SRH was associated with more cognitive and functional impairments, more comorbid illnesses, and fewer years of formal education. That study also noted that persons with poor SRH were 138% more likely to die after 5 years than were participants describing better SRH.
Epidemiological studies of older adult drivers report associations of driving cessation with medical diagnoses as well as subjective and objective functional, visual, and cognitive impairments which probably influence older adults' assessments of their health (4–10,12). One study compared active older drivers to former drivers with and without current driver licenses. Individuals who had active licenses but were no longer driving had worse SRH than individuals who continued to drive; those who did not renew their licenses were less healthy than former drivers with active licenses (19). In a cross-sectional survey of community-dwelling older adults, "medical problems" and "changes due to aging" were given as the principle reasons for driving cessation, and these individuals were twice as likely to report fair or poor SRH as active drivers. Whereas persons who stopped driving had fewer medical diagnoses, they described worse overall health, and were generally older than current drivers (11). In a secondary analysis of data on 2046 Californians aged 
55 years, Ragland and coauthors (20) noted that participants who avoided driving described having poor vision and functional impairments. Older women, in particular, reported that, among several reasons for limiting or avoiding driving, poor eyesight was the most prominent. Freeman and colleagues (21) and Stutts (9) noted the strong association of measures of visual function with driving cessation. However, when multiple covariates were taken into account in this and other reports, visual acuity did not retain statistical significance (8,14).
The current study also confirms the findings reported by Anstey and coworkers (14) in an American cohort using a similar study design and variables, such as measures of visual acuity, cognition, sociodemographic factors, and SRH. However, our study included additional measures shown to predict mortality and incident functional disability—the CCI, a validated index of overall health, and the SPPB (17,18).
The overlapping of the ROC curves of the three predictors—SRH, CCI, and the SPPB—suggests that the simple, easily ascertained SRH should be considered as an important trigger early in the physician–patient encounter. At these times, physicians can request a simple statement regarding overall health from their older patients. For patients with poor or fair SRH, this could lead to a search for modifiable risk factors that might contribute to decisions about driving. When feasible, the remediation of modifiable factors in patients reporting poor to fair SRH could result in seniors continuing to drive safely and thereby maintaining their independence. This approach will be particularly important in rural states like Alabama, where alternative transportation sources are unavailable. In support of this view, Tinetti and colleagues (22) noted that five potentially modifiable impairments, involving the lower extremity, upper extremity, vision, and affect, contributed between 17% and 23% to incident declines over 3 years among a cohort of older adults. The interrelatedness of risk factors among some geriatric syndromes suggests that the benefits of remediation may extend to other adverse outcomes common to older adults (23).
This study has several limitations: Although the SOA included questions about driving, it was designed to assess trajectories of mobility change in older African Americans and whites (15); specific reasons for driving cessation were unavailable. Additionally, because SOA participants were rural- and city-dwelling Alabama residents, the generalizability of these findings to other populations remains uncertain. An intervening factor may have been a worsening of overall health status over the 2-year observation period. If this occurred at random, the observed ORs underestimate the association of SRH and driving cessation. Nevertheless, older adults appear to have a realistic sense of their own health status and its impact on lifestyle factors such as driving.
Conclusion
Self-reported health was an independent predictor of driving cessation in community-dwelling older drivers. SRH can be easily assessed during routine clinic visits to identify at-risk older adults, and may be as powerful as the CCI and the SPPB in predicting driving cessation.
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A poster describing the current study was presented at the 2005 Annual Meeting of the American Geriatrics Society, Orlando, FL.
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Received June 29, 2006
Accepted October 5, 2006
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