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Correspondence: Address correspondence to David R. Ragland, PhD, MPH, University of California Traffic Safety Center, University of California at Berkeley, 140 Warren Hall, Berkeley, CA 94720-7360. E-mail: davidr{at}uclink4.berkeley.edu
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Key Words: Automobile Driving • Aged • Health • Vision
It is well known that the frequency of driving declines with increasing age, especially at night and during periods of high traffic volume (Stewart, Moore, & Marks, 1993). There is also evidence that women are more likely than men to stop driving (Campbell, Bush, & Hale, 1993; Stewart et al., 1993). It is important to determine the reasons for a decline in driving with increasing age. It is important, for example, to determine whether a decline in driving is associated with medical conditions or functional limitations, or whether instead a decline in driving is associated with a change in the need for mobility. With information on physical, social, and psychological factors affecting driving, we might be able to design interventions that extend the years of safe driving in older populations.
A number of studies of factors leading to limitations or cessation of driving have been published in recent years. These have been characterized by two different approaches. One approach has been to measure driving outcomes and various medical and functional status variables separately, and then to link medical–functional status variables statistically with driving outcomes (drivers vs. exdrivers, miles driven per week, and difficulty with driving; see Ball et al., 1998; Brayne et al., 2000; Campbell et al., 1993; Cotrell & Wild, 1999; Gallo, Rebok, & Lesikar, 1999; Kington, Reuben, Rogowski, & Lillard, 1994; Lyman, McGwin, & Sims, 2001; Marottoli et al., 1993; McGwin, Chapman, & Owsley, 2000; Stewart et al., 1993; Stutts, 1998). All of these studies, with the exception of one by Cotrell and Wild (1999), where vision was not measured, found that driving outcomes are associated with one or more vision problems or with medical conditions affecting vision (e.g., cataracts). Most of these studies also found that driving outcomes are associated with various cognitive impairments or with medical conditions causing cognitive impairments (e.g., stroke, Parkinson's; see Campbell et al., 1993; Cotrell & Wild, 1999; Gallo et al., 1999; Kington et al., 1994; Lyman et al., 2001; Marottoli et al., 1993; Stutts, 1998).
Another approach has been to simply ask people directly whether there are factors that have led them to limit or cease their driving (Dellinger, Sehgal, Sleet, & Barrett-Connor 2001; Hakamies-Blomqvist & Wahlstrom, 1998; Johnson, 1995, 1998; Kosnik, Sekuler, & Kline, 1990; Persson, 1993). Each study using this approach has focused on people who had stopped driving or who had failed to renew their driver's license. Impaired health and medical conditions were prominent factors in each case. One study focused exclusively on vision (Kosnik et al., 1990), finding that a range of vision deficits were related to limited driving. A factor mentioned in three of the studies was feelings of stress and insecurity about driving. Gender differences also have been noted, with men more likely than women to report medical reasons and women more likely to cite feelings of stress and avoidance of difficult driving situations (Hakamies-Blomqvist & Wahlstrom, 1998).
Both approaches to assessing reasons for limitations or cessation of driving are important, and they supplement one another. Statistically linking medical conditions–functional status and driving outcomes permits assessing the "risk" of driving cessation or limitation associated with particular conditions. Directly asking people about reasons for limitations or cessation of driving allows an assessment of how different medical or functional conditions are viewed in relation to driving cessation or limitation. Differences in patterns between the two may reflect, for example, differences in awareness of the impact of various conditions. In addition, directly asking people permits assessment of perceptions and motivations (e.g., lack of confidence or fear of an accident) that may mediate the relationship between medical–functional conditions and driving outcomes.
The current study, using data from the Study of Physical Performance and Age-Related Changes in Sonomans (SPPARCS), is an analysis of a series of questions asking people directly whether there are factors that have led them to limit or cease their driving. The study extends previous research by including specific questions on a number of different medical conditions as well as a number of questions on nonmedical reasons. In addition, the study also examines the extent to which differences in these reasons vary by living arrangements and family income. It was hypothesized that living arrangements and household income may be associated with both demand (i.e., the need to drive) and resources for driving. Those who live alone may be more likely than those who live with others to drive, even in the face of health and physical difficulties. In contrast, those who live with others and those with higher income may have more resources than others to drive. Finally, the study examines the extent to which differences in these reasons vary by comorbidity, functional status, cognitive status, and direct and self-reported measures of vision. It is hypothesized that these factors will influence both medical and nonmedical reasons for driving limitation or cessation.
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Methods |
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The present analysis is based on data from the baseline assessment of the SPPARCS cohort. Selected characteristics of the sample are presented in Table 1. The sample was restricted to those participants who reported whether they limited or avoided driving (n = 2,046; 32 proxy interviews excluded).
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The individuals in the sample are also somewhat more affluent and educated than Sonoma residents aged 55 and older. A comparison of the sample with California residents aged 55 and older indicates that the modal income category of our sample ($25,000–49,000) is the same as the modal income category for the entire state. Furthermore, there is very little difference in the percentage of households with annual incomes of $50,000 or more (55–64 years, sample 44%, state 39%; 65–74 years, sample 23%, state 20%; 75+ years, sample 13%, state 12%). The only residents who were underrepresented in the sample were those with household incomes of less than $10,000. To the extent that income is associated with driving, the prevalence of driving and driving greater distances is probably somewhat greater in this sample than in older populations with larger percentages of lower income residents.
Reasons for Limitation or Avoidance of Driving
Participants were asked their current driving status (current drivers, former drivers, or never drivers). They were also asked whether they limit or avoid driving for any of a series of common reasons (see list in Table 2). These included 14 medical reasons, including a physician's recommendation or a family recommendation, and 7 nonmedical reasons.
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Living Arrangements
Participants were asked about the number of other persons who live with them and the relationship of each household member to the participant. Categories included "lives alone," "lives with spouse with or without others," and "lives with nonspouse others."
Functional Limitations
Participants were asked if assistance was necessary or if they experienced difficulty with the following activities: walking up or down a flight of stairs, walking three neighborhood blocks, or lifting a 10-lb (4.53-kg) object. An index was created that consisted of a count of the number of such limitations reported.
Medical Conditions
Respondents were asked if a doctor had ever told them they had any of the following conditions: cancer, diabetes, heart disease, high blood pressure, arthritis, or stroke. An index was created that consisted of a count of the number of conditions reported.
Cognitive Function
Cognitive function was assessed by a modified Mini-Mental State Examination (MMSE). On the basis of a pattern of responses, a subset of six items was selected to provide the most sensitive measure of cognitive function for this sample. The six items included the questions and tasks in which 10% or more of the participants responded or performed incorrectly. The values were grouped into the lowest quartile (scores 0–14) and upper three quartiles (scores 15–18).
Visual Function
Visual function was measured with the Smith–Kettlewell Institute Low Luminance (SKILL) Card. The SKILL Card is a clinical test, which captures visual function under low-contrast and low-light conditions. It is a particularly sensitive measure for function as a result of certain visual impairments (e.g., optic neuritis, glaucoma, or maculopathy), some of which are age-related impairments. The test has also shown strong correspondence with driving performance in older populations. In addition, respondents were asked to provide an overall assessment of their vision, comparing their vision with that of other people their age (i.e., "better than most, about the same as most, or worse than most").
Analysis
The pattern of driving status by age was evaluated with a chi-square statistic and calculated separately by gender. The pattern of reasons for limiting or avoiding driving by age was also evaluated with a chi-square statistic, both for each of the 21 reasons separately and then for each of the two combined categories of limitations (medical or nonmedical). Finally, logistic regression was used to evaluate the relationship among age, income, and living arrangements and each of three categories of reasons (i.e., medical, nonmedical, and either medical or nonmedical).
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Results |
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Table 2 reports the reasons given by the licensed drivers for limitation or avoidance of driving. The results are reported separately for each of 21 reasons by age and gender. "Problems with eyesight" was the leading reason reported by respondents, especially for women. The percentage reporting this reason also increased with age for both men and women. Nearly 40% of the women aged 75 and older reported vision problems, compared with about 29% of the men in that same age group. In addition to vision problems, there were two nonmedical reasons that were listed by both men and women. These reasons included being "concerned about being in an accident" and having "no reason to drive," and percentages reporting these reasons increased by age for both men and women. Women also reported a concern about crime as a leading reason for limiting or avoiding driving, and the percentage increased with age. In contrast, men were much less likely to identify crime as a leading reason.
Participants in the study reported an average of 0.4 medical reasons for limitations of driving (range 0–6), 0.5 nonmedical reasons for limitations of driving (range 0–6), and 0.9 medical or nonmedical limitations (range 0–10). Figures 1 and 2 report summary categories by age and gender. Information is provided on the percentage of individuals who give at least one limitation in each category. For all three categories (medical, nonmedical, and at least one of either), female respondents report more limitations than male respondents at each age category. In all cases there is a steep age gradient from younger to older age categories for both the percentages reporting at least one reason.
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For both female and male respondents, comorbidity had a small association with both medical and nonmedical limitations, but the association was significant only for women. For women, functional status was strongly associated with reporting medical limitations but not nonmedical limitations. For men, functional status was very strongly associated with reporting medical limitations and less strongly associated with reporting nonmedical limitations. For both women and men, cognitive function had little or no association with either medical or nonmedical conditions.
For both women and men, objectively measured vision (SKILL test) had a small but not significant association with the reporting of both medical and nonmedical limitations. For both women and men, reporting that vision was "about the same" as that of others of comparable age (as opposed to "better") was not significantly related to reporting either medical or nonmedical limitations. However, for both female and male participants, reporting that vision was "worse" compared with that of others of comparable age was highly associated with the reporting of medical limitations. Reporting that vision was "worse" was not significantly associated with the reporting of nonmedical limitation for either female or male participants.
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Discussion |
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Nonmedical reasons, such as being concerned about being in an accident and having no reason to drive, were also cited. The concern about being in an accident may be due to a variety of factors, including concern about insurance, repair expense, and possible injury and disability. Of course, this concern also may be due to a particular health or medical condition. Reports of having no reason to drive deserve special attention. People who gave this reason may have a reduced need for specific goods and services; their access to goods and services may not depend on driving (i.e., within walking distance or access to mass transit); or they may be able to call on others to drive. It may be, for example, that people who give this reason are more likely than others to live with a spouse who drives.
Unlike the other reasons, the most distinctive difference between men and women is the topic of crime. Women are much more likely than men to cite a concern about crime as a reason to limit or avoid of driving. This concern may limit outside activities in general.
Although there is a variety of reasons for limitation or avoidance of driving, the age and gender patterns are generally similar. Nevertheless, in general, women are more likely than men to report one or more reasons, regardless of the type of reason. In addition, the likelihood of citing one or more reasons increases with age.
Predictors of Reporting Medical and Nonmedical Limitations
Household income was a significant predictor of reasons to limit or avoid driving. With the exception of medical reasons for men, those with lower income are more likely than those with higher income to cite reasons for limitation or avoidance of driving. There are a variety of possible explanations for this. For those with lower incomes, the medical and nonmedical reasons cited by respondents may be more severe. Older people with lower incomes may have fewer resources and be more vulnerable than older people with higher incomes. As a result, medical and nonmedical factors may be more likely to disrupt the driving of older people with lower incomes. It also may be that the driving conditions of lower income older people are more demanding (e.g., having to drive longer distances under more difficult circumstances.)
Contrary to our predictions, living arrangements (live alone vs. spouse, and lives with other vs. spouse) was not an important predictor of either medical or nonmedical reasons for limitations in driving.
Comorbidity had a small association with both medical and nonmedical conditions (although it was not significant for men). Both reported medical and nonmedical reasons for limitations in driving are affected at least to a small degree by major medical conditions.
Surprisingly, an objective measure of vision (the SKILL test) was also not related to either medical or nonmedical outcomes. However, reporting that vision was "worse than" the vision of others of comparable age was highly associated with reporting medical limitations of driving. This suggests that an overall, perceived assessment of vision is more important in limiting driving than an objectively measured assessment of light and dark acuity.
Functional status was fairly strongly associated with medical limitations for driving. Functional status may represent the "common pathway" between medical conditions and reported limitations in driving. Functional status also tended to be associated, but less strongly, with nonmedical limitations. This means that, to a small extent, nonmedical limitations for driving are affected by functional status. Surprisingly, cognitive functioning was associated with neither reported medical nor nonmedical limitations. Those with reduced cognitive function may be less aware of limitations or less likely to report driving limitations.
Relationship to Previous Studies
The current study is consistent with other studies, described in the introductory paragraphs, in that having problems with vision is a major factor contributing to limitations in driving. However, in the current study, factors associated with cognitive function (e.g., problems with balance, feeling confused, or difficulty concentrating) were not frequently mentioned as reasons for limiting driving. There are two possible reasons for this discrepancy.
The first reason may reflect a difference in prevalence between vision and cognitive problems in the Sonoma study. In each of the other studies linking driving variables and medical conditions statistically, the driving outcome variable among those with a particular medical–functional status condition is compared with the driving outcome variable among those without the medical–functional status condition; that is, prevalence is not taken into account. In the current study, prevalence is an integral part of the outcome; that is, the statistic used is the percentage of participants that mention a particular condition. It seems important in future studies to include information on the prevalence of various conditions associated with limitations or cessation in driving in addition to the level of limitation among such conditions. In this way both the relative risk and the attributable risk of a particular medical condition can be assessed.
A second reason may reflect a difference in awareness of vision versus cognitive problems. In a study by Cotrell and Wild (1999), patients with Alzheimer's disease may not restrict some dimensions of their driving voluntarily, and this failure may be associated with an awareness deficit. Indeed, a critical dimension of dementia may be lack of awareness of one's cognitive deficits (Gil et al., 2001). In contrast, a study by Kosnik and colleagues (1990), showing that older adults who had recently given up driving reported more visual problems, suggests that people may be aware of their vision deficits and that this may affect decisions about driving behavior. The level of awareness of various conditions that affect driving may be a very critical area for future research.
The fact that vision is an important factor in both kinds of studies described in the introductory paragraphs (i.e., studies linking driving variables and medical conditions–functional status statistically, and studies asking people directly about the link between various conditions and driving behavior) is noteworthy. Several of the studies identify particular dimensions of vision. For example, Kline and colleagues (1992) identified "dynamic vision, visual processing speed, visual search, light sensitivity, and near vision" (p. 31) as important factors. It is clearly important to systematically evaluate different dimensions of vision impairment in relation to driving limitations.
Comparison of Driving With Other Activities
Although vision problems represent an apparent barrier to driving, it would be incorrect to assume that poor vision represents a barrier to all outdoor activities. In a recent study, reported limitations or avoidance of leisure-time physical activity in the same sample of Sonoma residents was shown to be associated with a variety of medical and nonmedical factors (Satariano et al., 2000). Nonmedical factors, such as disinterest, concern about crime, and the absence of an exercise companion, were associated with a 20% to 30% reduction in the number of respondents who reported engaging in physical activity at the recommended levels. In addition, unlike the results for driving, the results for physical activity suggest more of a difference between men and women. Women aged 55 to 64 were more likely than men of the same age to report that not having an exercise companion was a leading reason for the limitation or avoidance of physical activity. Similarly, nearly one third of women aged 75 and older still reported that the absence of an exercise companion was a significant barrier to regular physical activity (Satariano et al., 2000). No doubt, this finding reflects the fact that women are more likely than men to live alone. With increasing age, men and women were more likely to report medical conditions and a fear of falling.
Implications for Research
The combined results of the present study and previous studies suggest several important areas for research on the factors that lead to limitation or cessation of driving. Important areas of research include the following: (a) types of vision problems that lead to reported limitation on or avoidance of driving; (b) types of cognitive deficits that lead to reported limitation or avoidance of driving; (c) relative awareness of, and appropriateness of, driving adjustments, in response to vision versus cognitive impairments; (d) importance of nonmedical reasons for limitations or avoidance of driving; (e) examination of each of these questions as they vary by age and gender; and (f) examination of these questions in other sections of the United States and among older people of different socioeconomic positions and among people in different racial and ethnic groups. It is expected that research in these areas will improve our understanding of the barriers to driving and, more generally, access to goods and services that are experienced by older people.
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Footnotes |
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1 University of California Traffic Safety Center, Berkeley.
2 School of Public Health, University of California at Berkeley.
Decision Editor: Laurence G. Branch, PhD
Received for publication May 6, 2002. Accepted for publication September 16, 2002.
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