Section 12: Psychiatric Diseases

Mental illness is relatively common, with recent studies suggesting that roughly one-third of the general population exhibits signs of mental illness sometime during their lifetime (Weiten, 1998). Earlier estimates were much lower, with indications that one-fifth of the population would exhibit signs of mental illness sometime during the life span (Neugebauer, Dohrenwend, and Doherenwend, 1980). The current estimates are much higher due to the recent inclusion of substance abuse disorders as a category of psychiatric illness. Before 1980, substance abuse disorders were vaguely defined in the first two editions of the Diagnostic and Statistical Manual of Mental Disorders (DSM), manuals published by the American Psychiatric Society and used to categorize psychiatric disorders. However, in 1980, with the advent of the DSM-III, explicit criteria for substance abuse disorders were introduced, resulting in more effective recording of substance abuse (American Psychiatric Association, 1980).

A summary of the current fitness-to-drive guidelines (Psychiatric Diseases) for medical practitioners from Australia (1998) and Canada (2000) is presented in Table 33.

As noted above, psychiatric disorders are relatively prevalent in the general population. Some of the more common psychiatric disorders include mood disorders (depression, bipolar disorder), anxiety disorders, schizophrenia, and other psychotic disorders, such as delusional disorder, delirium, dementia (including Alzheimer's disease), and substance abuse disorders(National Institute of Mental Health, 1999). Recent statistics indicate that of adult Americans 18 and older, more than 19 million suffer from a depressive illness each year, more than 2.3 million Americans suffer from bipolar disorder, more than two million are affected by schizophrenia, and more than 16 million adults (ages 18 to 54) suffer from anxiety disorders (National Institutes of Health, 1999).

Despite the prevalence of psychiatric disorders in the general population, there have been few investigations into the relationship between psychiatric illness and motor vehicle crashes. Surprisingly, the majority of the research that is available was conducted, on average, more than 30 years ago. Because of the paucity of recent literature, the older literature will be described below, followed by a review of the most recent literature. A summary of the results is provided in Table 32.

In one of the earliest studies, Waller (1965) distributed questionnaires to individuals with known psychiatric conditions based on reports from the California Department of Motor Vehicles. Questionnaire data also were obtained from a random sample of drivers seeking driver's license renewal. Results revealed that those with reported psychiatric disorders drove fewer miles per year but had double the crash rate compared to the comparison sample. Methodological limitations of this study include a biased patient group (i.e., only those patients reported to the Department of Motor Vehicles by physicians), unknown diagnostic criteria (e.g., not standardized DSM criteria), and crash rates based on self-report.

Table 32  Summary of the Research Literature on Psychiatric Conditions and Motor Vehicle Crashes