Epidemiologic Issues About Alcohol, Other Drugs and Highway Safety

Transcription

1 Epidemiologic Issues About Alcohol, Other Drugs and Highway Safety Julian A. Waller1 One cannot help but feel a sense of frustration in any discussion about alcohol, other drugs, and highway safety. Although new psychoactive drugs are still being discovered both alcohol and other basic mind altering chemicals have been known and used since antiquity. In the case of alcohol, there is now wide and virtually unanimous agreement that ingestion does contribute substantially to highway crashes But there is still some argument regarding the circumstances and extent of the contribution, and considerable confusion about appropriate countermeasures. As far as other common drugs such as marihuana, barbiturates, tranquilizers, and opiates are concerned, there is no agreement as to whether a safety problem exists or what to do if it does. It is not my intention to repeat the extensive and convincing data about alcohol. Nor will I attempt to catalogue pharmacologic effects of various other drugs or try to predict how these effects might relate to possible phenomena on the highway. That has been done in the past, and it is now time to move on to other considerations. Therefore, this paper will be concerned with identifying several epidemiologic principles and their applications, and with a specific discussion of some recent data about marihuana, one of the most common drugs in current use. I feel that this approach is warranted for several reasons. First, we are not involved in studying this problem simply out of scientific curiosity, but rather for administrative ends. As long as there is a shortage of resources, either for research or for action, we have a responsibility to direct our attention, wherever possible, to those parts of the phenomenon that currently appear to create the greatest social problem, or to have the greatest likelihood of creating a major problem in the future. Therefore, some guidelines are needed to suggest how to set priorities in research and action. Second, social phenomena are the result of many interacting forces and commonly vary over time and from one geographic or cultural area to another. An international meeting provides a good opportunity for discussion of these differences. Third, while reviewing recent papers from the epidemiologic viewpoint, I have been disturbed by some of the methodologic errors that are apparent. These errors, however, are not being brought to the attention of the many people who are exposed only to the conclusions of the work, and who consequently may be left with erroneous information because they know nothing of the methodology. 1 Professor and Chairman, Department of Epidemiology and Environmental Health, University of Vermont, Burlington, Vermont, U.S.A. 3

2 4,/. A. Waller THE FREQUENCY QUANTITY MODEL Let us examine first the question of setting priorities. It is my contention that all drugs are not equal in potential hazard; nor are all users of these drugs; nor all circumstances of use. Where should we look first? I believe this question can be answered by means of a model of frequency and quantity of deviant behavior. In this case, deviant behavior is defined as behavior which has high risk of initiating social problems. Now it is important to note that, with very rare exceptions, a perfect correlation does not exist, either with physical or biologic phenomena, between the presence of a cause or causal set and the occurrence of an effect. However, the stronger the causal set the more likely it is that the effect will occur, and the greater it will be. As applied to drugs and highway safety the frequency-quantity model of deviancy, therefore, states the following: a) The more frequently a drug is used in the highway setting the more often it is likely to be a problem. b) The more impairing the effect of the drug, either because of its inherent nature or because of the usual quantity consumed, the more likely there is to be a problem. Therefore, a drug (for example, caffeine) that is used frequently but is not impairing unless used in great quantity, will not create a serious problem. Nor will one that is impairing but that is consumed relatively infrequently by many or relatively often but by few. Among the many potential problem drugs the only ones that will create a problem of large proportions are those that simultaneously have high prevalence of use and relatively high quantity of impairment under the circumstances of use. How many drugs on the North American continent meet these criteria at this time? Clearly alcohol does, both because of its frequency of use and the severe impairment that is associated with excessive use. As the use of marihuana and hashish has been on the increase among teenagers and young adults it may be asked if these drugs meet the criteria. They may meet the first, but since it is difficult to measure the level of impairment one cannot tell if they meet the second. Tobacco might be another possibility. It is widely used; it is commonly used in conjunction with alcohol (18), it is known to be associated with some cardiovascular impairment (14), and the levels of carbon monoxide generated are known to create mild impairment of cerebration (4). A few years ago we examined carboxyhemoglobin concentrations (COHb) and blood alcohol concentrations (BAC) among drivers fatally injured in crashes (18). We also estimated COHb based on smoking history, and we recorded BAC among drivers not in crashes but who were interviewed at times and places where fatal crashes had occurred. Compared to persons with a BAC of <20 mg/100 ml and COHb <5%, those with COHb >5% were overrepresented about 3 times among the fatalities, and those with COHb >5% plus a BAC of <20 mg/100 ml overrepresented even more. Alcohol and COHb appeared to have an additive effect in this overrepresentation. These data appear in Table I. Because the methods of collection were not entirely comparable, however, the results are only preliminary. Also, we do not know whether this possible overrepresentation might apply to all crashes, or only to fatalities in which the reduced oxygen-carrying capacity of blood might adversely affect the ability to survive. However, others have found similar moderate overrepresentation of smokers in crashes of all degrees of severity, although the other

3 Epidemiologic Issues 5 studies have not controlled for the relationship between smoking and drinking behavior (1). TABLE I BAC (mg/100 ml) Blood alcohol concentration, carboxyhemoglobin and risk of fatal crash COHb (%) Relative Risk <20 <5 1.0 > <5 1.8 >5 3.8 >100 < > I do not believe that at this time there is any other drug in North America that meets both criteria, although for a brief time LSD appeared to be a possible candidate. In other cultures, additional drugs might be a problem. One recent phenomenon in the United States exemplifies the model. In many states the legal age for alcohol consumption has recently been reduced from age 20 or 21 to age 18. Some have predicted that this would increase the prevalence of exposure and thus cause a rise in the crash problem. Others, including myself, have suggested that data show that exposure among persons age 18-20, albeit illegal, was already the rule rather than the exception, and, therefore, we did not predict a sudden surge of alcohol related deaths. Data now available from several states show that there has been an increase in frequency of alcohol use among teenagers in those areas that had previously enforced alcohol limitation by age in rigorous fashion (7). According to one report (21) this increase can be converted into about three additional deaths annually per 100,000 persons age In those geographic areas that previously had lax enforcement of drinking laws, however, such an increase has not occurred (7). MEASURING THE OCCURRENCE AND EXTENT OF THE PROBLEM Next, let us turn to some of the factors that may affect not only the occurrence of a problem in different cultures, geographic areas, and at different times, but also the perceptions of the extent of the problem. Any epidemiologic study must consider these and related factors if it is to be usefully applied in more than one setting. The actual definition of a highway fatality is one such issue. How can we compare fatality rates between nations if in one country a person is not defined as a highway fatality unless he died at the crash site, in another all deaths within the first 24 hours are counted, in still others deaths in the first week are included, in several countries the criterion is death within 30 days, and in the United States those who die of their injuries after up to one year may be counted? I urge the establishment of a task force to develop appropriate correction figures and to update these periodically so that we can begin to have some way of comparing this most basic measure of the highway crash problem from one nation to another.

4 6 J. A. Waller Another issue is brought up by the following question: If alcohol is a factor in about half of the fatal crashes, why does Israel, with a low rate of alcohol abuse, have one of the highest highway fatality rates in the world?. There are several answers. First, despite the assertion (which I personally suspect is correct) that alcohol is seldom a factor in Israeli crashes, I have seen actual data systematically collected from Israel to verify the assumption. One need only remember that for many years we heard similar assertions about the small role of alcohol in the United States and Canada and therefore have become cautious about jumping to premature conclusions. Modern Israel consists of several cultures, and different drinking patterns seem to exist even among Jews. Thus, we still await definitive data about the extent of alcohol involvement in Israel as well as in several other countries. Of equal importance is the reference I made earlier to causal sets. We know that single causes of a disease seldom exist, that even if one cause is predominant, or even a sine qua non, other causes commonly contribute both to frequency and severity. There are a few causes of this type that may contribute to the crash fatality problem in Israel. These, of course, may be applicable in varying degrees and combinations to other countries as well. One is the large number of new, inexperienced, and perhaps also relatively young drivers. Such populations commonly have high crash rates even in the absence of alcohol. Furthermore, because they have not yet internalized driving skills and judgments they are exceptionally sensitive to impairment by relatively small amounts of alcohol. Thus, with use of alcohol being common but abuse uncommon, alcohol may provide a moderate contribution to the highway crash rate in Israel. Another probable contributor is the environment. Roads in Israel tend to be two lane, narrow, winding, and bordered closely by rocks. The size and mechanical condition of the vehicles varies tremendously and the drivers are from widely disparate cultural backgrounds. Desperation passing is not uncommon under these circumstances, and the environment is extraordinarily unforgiving of any errors of judgment whether because of alcohol or for any other reason. In short, I am suggesting that the time has passed when we could be satisfied with doing epidemiologic studies of the contribution of alcohol alone. Rather, especially for international comparison, we need to know the nature and extent of other factors that simultaneously contribute to the problem. There have been extremely few such studies. Results of laboratory and simulation studies are reasonably transferable from one country to another. Work involving epidemiology in the field, however, is often not comparable unless all of the major contributing factors are well defined. EVALUATION PROGRAMS Yet another epidemiologic issue is the evaluation of programs and demonstration projects. The U.S. Department of Transportation is now completing a multi-million dollar demonstration program called ASAP, or Alcohol Safety Action Projects. ASAP in the American jargon also means as soon as possible ; and in the political tradition of federal programs, that philosophy seems to have prevailed among most but not all who gave the program direction. The evaluative studies (2) that are now being published suggest that, compared to the baseline period before these projects began, there has been improvement in the countermeasure areas in some aspects of the alcohol crash problem. Unfortunately, these studies did not include consideration of what might be happening during the

5 Epidemiologic Issues 7 same time period in areas without countermeasures. In a recent report (23) from the Insurance Institute for Highway Safety, an attempt has been made to provide such a comparison and it has been concluded that the same changes were occurring in other communities without countermeasures as in the communities with countermeasures. There has been some argument whether the right communities were chosen for comparison (3). However, the important question is not whether the right comparison was chosen retrospectively, but why no attempt was made to build in such a comparison initially. I believe I can answer this question. One ASAP project, our own Project CRASH in Vermont, does have the necessary two by two design with baseline and followup data in both countermeasure and comparable comparison areas. We were able to incorporate this design into the project and to maintain the design only by constant struggle against very great pressures from federal government, within the state, and even within the project. Our data were not included in the Department of Transportation report, and we are not yet ready to present completed results, although there are several promising aspects of our preliminary results. The point, of course, is that evaluation is one of the most important current uses of epidemiology, and that there is no satisfactory substitute for the two by two evaluation design and none should be attempted. Yet, after 75 years of action without evaluation, we still do not appear to have learned the necessary lessons. Another lesson to be learned concerns the use of data containing false negatives and false positives. A person who survives for hours or days after injury may have no alcohol in his blood at time of death, not because he hadn t been drinking, but because the alcohol he consumed had long since been metabolized. When these survivors are included in data about people who do or do not have alcohol a very high proportion of false negatives occurs. Therefore, most studies of the presence of alcohol are now limited to persons who died within six hours after injury and to persons aged 15 or older. Zylman (24) has correctly pointed out, however, that one effect of excluding persons who survive for more than 6 hours is to overload the excluded group with elderly persons who tend to have alcohol less often than the rest of the population. I estimate that this error probably results in less than a 4-5% overinflation of the role of alcohol in highways crashes. However, as in the case of death rates discussed earlier, the techniques of standardizing the result by means of age correction are well known, and I would urge that an ad hoc committee be formed to present the 7th conference on alcohol drugs and traffic safety with appropriate guidelines for applying such corrections in future reporting. Unfortunately, in describing the problem of excluding the elderly, much of Zylman s discussion leaves the impression that exclusion of persons who died six hours or more after injury is entirely inappropriate no matter what the age group. Other errors in Zylman s work include the failure to distinguish in his analyses between persons who initiate crashes and those who are innocent victims. The Distilled Spirits Council of the United States (DISCUS) has given his statements such wide publicity, suggesting that alcohol is nowhere near the problem that the scientific community has been saying it is, that it has become imperative that his methodologic mistakes be given equally wide publicity. Another place where this error of false negatives occurs is in the correlation between high BAC and fatty changes of the liver. As pointed out in our original paper (16) on this subject, persons under age 25, no matter how serious a drinking problem they might have, are extremely unlikely to have visible fatty changes of the liver.

6 8 J. A. Waller Therefore, because of the high likelihood of false negatives in this age group, any attempt to correlate fatty changes and problem drinking among persons with BACs of 100 mg/100 ml or higher must be limited to those age 25 or older. Zylman (25) and others (20) have not done this and, therefore, in my opinion have reached erroneous conclusions about a lack of correlation. MARIHUANA AND HIGHWAY SAFETY Finally, let us examine what is known from the epidemiologic viewpoint about marihuana and its products and highway safety. Ideally, it would be useful to be able to compare actual concentrations of tetrahydrocannabinol (THC) or other drugs among persons who have just been involved in crashes of various types and among drivers exposed to similar circumstances of time and place but not involved in crashes. This type of design, of course, was first reported in studies of alcohol by Holcomb (9) in 1938 and was brought to fruition with the work of Haddon and his associates (8,10), and by Borkenstein and his associates (5). To my knowledge, it has not been repeated perfectly with any other drugs. However, in some cases for example, with tranquilizers and barbiturates enough data exist concerning the usual prevalence of these drugs in the population. Thus it is fairly apparent from the several studies of the part played by these idrugs in highway fatalities that they are not substantially overrepresented in the cause of fatalities (11, 17). With marihuana, however, there are different problems. First, a truly adequate method of testing for THC in the blood does not exist. The techniques currently being used by Midwest Research Institute (22), under contract with the U.S. Department of Transportation, still appear to have possible substantial problems involving false negatives and false positives. Also, there are no really accurate data about the prevalence of marihuana use, especially in relation to driving; and whatever the prevalence is, it appears to be changing from one year to the next. Yet another problem is the reported shift in use patterns from consumption of marihuana alone during the 1960s to frequent consumption in combination with alcohol during the 1970s. Thus, even if crashes were found to be overrepresented among marihuana users who also used alcohol we would have to ask whether the overrepresentation was attributable to the marihuana, to the alcohol, or to both. There are some studies which may bring us a bit closer to answering these questions. Several years ago, for example, I studied annual crash rates per unit miles travelled among persons with various potentially impairing conditions including illegal use of drugs, and among drivers of similar age and sex without such conditions (15). It was concluded that drivers using marihuana and various other drugs did not have an increase in crash risk. Other work by different researchers (12) has supported this conclusion for all except persons addicted to amphetamines. In the absence of a method to actually test for marihuana we turned to a more sophisticated version of the 1966 study, which now involved the driving experience of two freshman classes at the University of Vermont. Freshmen were given a national student profile questionnaire which most completed shortly after arrival at school. We gave all students participating in this profile an additional questionnaire about marihuana, alcohol, and other drugs and driving which they completed anonymously and returned before they left the testing center. Ninety-seven percent of the students completed this questionnaire, giving us a sample of over 1200 students in 1972 and over 1500 the next year. Only the results will be discussed here rather than the

7 Epidemiologic Issues 9 methodology. We do have good reason to believe, though, that the answers we received were an honest attempt by the students to describe their experiences. In 1969 a study (13) showed that 28% of all students on the University of Vermont campus used marihuana in the previous year. By 1972 this had risen to 49% of the freshman class and by 1973 to 57% of freshmen. Only 11% of all freshmen, or 20% of users, were consuming more often than weekly, however. The following data are from the 1972 study (19). Among users 47% did not drive at all or did not drive after using marihuana, and another 31% drove while high less than once a month. On the other hand, 11% of users reported that they drove several times a week while high. Most important, the heaviest users of marihuana were also the ones who most often consumed potentially impairing amounts of alcohol (i.e. 3 or more drinks) in conjunction with smoking and who drove after using these two drugs. Thus, persons who used marihuana daily represent 5% of users with drivers licenses, 33% of all driving trips after marihuana and 49% of driving after combined use of marihuana and 3 or more drinks of alcohol. What effect did users say marihuana had on their driving? Thirty-three percent reported no effect and 10% said it made them better drivers. However, 17% said it altered their time sense, 22% that it affected vision or attention span, and another 18% that it had other or combined effects. Users commonly reported that they drove more cautiously after using marihuana but less cautiously after using alcohol, an assessment that is consistent with some simulation studies (12). In the second study, we listed those who reported more cautious driving as a separate group. In the first study we identified a total of 4 crashes and 42 near crashes that were reported to have occurred under the influence of marihuana. About 60% of these appeared to be directly attributable to marihuana, and 27% to alcohol, while in the remainder the cause was not ascertained. Interestingly, drivers who reported that marihuana affected time sense only were less likely to have near crashes than were those who reported other negative effects, such as on vision or attention span. Because we did not have good information from the first study as to whether the crash and near crash rates after using marihuana were excessive or not, we collected information in the 1973 study about annual mileage, crashes, near crashes, traffic citations and occasions when these drivers almost got a ticket with and without use of marihuana. The second study is still being analyzed, but preliminary data are now available. Overall, 11% of annual mileage was reported to have occurred within 2 hours after using marihuana. Whether the criterion was crashes, near crashes, citations, or near citations the rates per unit mile travelled were similar for the 7.6 million miles without marihuana and the.9 million miles with the drug. As in the first study, we found important differences in near crashes after marihuana use according to the usual effect that the driver reported the drug had on him. Thus, the rate of near crashes without marihuana was 12 per 100,000 miles. With marihuana it was from 2-5 per 100,000 miles for those who said marihuana either had no effect or improved their driving, and from 5-13 for persons who had only altered time sense or who said the net effect was that they drove more cautiously. However, in keeping with the first study, among those who reported that marihuana adversely affects vision, attention span, judgment or causes combined effects, the near crash rate was 30 per 100,000 miles. These latter effects are the same that have been documented to occur with alcohol. It is possible, of course, that persons who are high on marihuana are less likely to be aware of or remember problems that occur while they are driving. Recent simulation studies (6), however, suggest that this is not the case. Assuming these data

8 10 J. A. Waller are reasonably accurate, how should they be interpreted in relation to the model of frequency and quantity of deviancy? First, although many people are using marihuana, the relative mileage is low considering that the data are from that age group representing most frequent users. Based on student statements, marihuana does have effects that are perceived by them to be impairing, but substantially less so than for alcohol. Nevertheless, several crashes and near crashes could be attributed to the effects of the drug per se. These do not appear to be sufficient in quantity to result in excessive risk at this time. Of particular concern, however, are those persons who report that marihuana adversely affects vision, attention span, or judgment. These are functions that are impaired by alcohol, and the combined use of alcohol and marihuana by such persons, in my opinion, cannot help but increase their crash risk. Thus, I would cautiously conclude that marihuana is likely to create a crash risk predominantly when used in conjunction with alcohol, a pattern that unfortunately appears to be increasingly popular. The impairment in this case would probably result from the combined effects of both drugs and would be most serious in persons who have similar types of effects from both drugs. SUMMARY Two problems currently relevant to the epidemiology of alcohol, other drugs, and highway safety have been considered. One is the need to set priorities for research and action; a model of frequency and quantity of deviancy has been proposed to provide a guide. Based on this model, only alcohol, marihuana and tobacco can be identified as of potentially major importance to highway safety at this time and on this continent, and alcohol appears to contribute to the hazard of the latter two. The other problem is the interspersing of the literature with data that are of unknown comparability. This includes varying definitions of a highway fatality, failure of studies to include environmental and other variables that may interact with alcohol and other drugs, evaluation studies that do not use a two by two design, and data that contain large numbers of false negatives and false positives. REFERENCES 1. Adams, J. R., Oral Habits and Traffic Accidents: Overdependency as an Explanatory Construct, Proceedings o f Fourth International Conference on Alcohol and Traffic Safety. Department of Police Administration, Indiana University, Bloomington, Indiana, 1966, pp Alcohol Safety Action Projects, Evaluation o f Operations 1972, Volume II, Detailed Analysis. Office of Alcohol Countermeasures, National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, D.C. 3. ASAP Effectiveness, National Traffic Safety N ewsletter, August National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, D.C. p Beard, R. R. and Wertheim, G., Behavioral Impairment Associated with Small Doses of Carbon Monoxide American Journal o f Public Health SI, 2012 (1967). 5. Borkenstein, R. F., Crowther, R. F., Shumate, R. P., Ziel, W. B. and Zylman, R., The Role o f the Drinking Driver in Traffic Accidents. Department o f Police Administration, Indiana University, Bloomington, Indiana, Dott, A. B., Effects o f Marihuana on Risk Acceptance in Simulated Driving Tasks. Injury Control Research Laboratory, Research Report 71-3, Providence, Rhode Island, 1971.

9 Epidemiologic Issues Douglass, R. L., and Filkins, L. D., The Effect o f Lower Legal Drinking Ages on Youth Crash Involvement Final Summary Report. National Highway Traffic Safety Administration, U.S. Department of Transportation, Washington, D.C., March Haddon, W. Jr., Valien, P., McCarroll, J. R., and Umberger, C. J., A Controlled Investigation of the Characteristics of Adult Pedestrians Fatally Injured by Motor Vehicles in Manhattan Journal o f Chronic Diseases 14, (1961). 9. Holcomb, R. L., Alcohol in Relation to Traffic Accidents, Journal o f the American Medical Association 111, (1938). 10. McCarroll, J. R. and Haddon, W. Jr., A Controlled Study of Fatal Automobile Accidents in New York City Journal o f Chronic Diseases 15, (1962). 11. Nichols, J. L., Drug Use and Highway Safety: A Review o f the Literature. Report DOT- HS U.S. Department of Transportation, Washington, D.C., Smart, R. G., Schmidt, W. and Bateman, K., Psychoactive Drugs and Traffic Accidents. Journal o f Safety Research 1, (1969). 13. Steffenhagen, R. A., Unpublished data from Project DART, Department of Sociology, University of Vermont, Burlington. 14. U.S. Department of Health, Education and Welfare, Smoking and Health, R eport o f the Advisory Comm ittee to the Surgeon General o f the Public Health Service. (PHS Publ #1103), U.S. Government Printing Office, Washington, D.C., Waller, J. A., Chronic Medical Conditions and Traffic Safety: A Review of California Experience. New England Journal o f Medicine 273, (1965). 16. Waller, J. A. and Turkel, H. W., Alcoholism and Traffic Deaths, New England Journal o f M edicine215, (1966). 17. Waller, J. A., Drugs and Highway Crashes Journal o f the American Medical Association 215, (1971). 18. Waller, J. A. and Thomas, K., Carbon Monoxide, Smoking, and Fatal Highway Crashes Proceedings o f Fifteenth Conference o f the American Association for A utom otive Medicine. Society of Automotive Engineers, New York, New York Waller, J. A., Lamborn, K. R., and Steffenhagan, R. A., Marihuana and Driving Among Teenagers: Reported Use Patterns, Effects, and Experiences Related to Driving. Accident Analysis and Prevention (in press). 20. Whitlock, F. A., Armstrong, J. L., Tonge, J. I., O Reilly, M.J.J., Davison, A., Johnson, N. G. and Biltoff, R. P., The Drinking Driver or the Driving Drinker? Medical Journal o f Australia 2, 5-16 (1971). 21. Williams, A. F., Rich, R. F., Zador, P. L., and Robertson, L. S., The Legal Minimum Drinking Age and Fatal M otor Vehicle Crashes. Insurance Institute for Highway Safety, Washington, D.C Woodhouse, E. J., The Incidence o f Drugs in Fatally Injured Drivers. Midwest Research Institute, Kansas City, Missouri. Final Report on Contract No. DOT-HS , U.S. Department of Transportation, February Zador, P., Statistical Evaluation o f the Effectiveness o f Alcohol Safety Action Programs. Insurance Institute for Highway Safety, Washington, D.C Zylman, R., Overemphasis on Alcohol May Be Costing Lives, Presented at 80th Annual Conference o f the International Association o f Chiefs o f Police, San Antonio, Texas, September 23, Zylman, R., Semantic Gymnastics in Alcohol-Highway Crash Research and Public Information. Journal o f Alcohol and Drug Education 19, 7-23, (Winter 1974).