German Study Confirms Grand Rapids Effects
A great deal of manipulation of the data, and even ignoring a HUGE portion of the data which would have made the complete study worthless had the ignored data contained even a small percentage of drinking drivers, the very best science from government produced the following REMARKABLE ADMISSION:
<<< For all BAC classes above 0%, we found 330 drivers in the accident study. Of those accidents, 213 were attributable to the effects of alcohol. By dividing those two numbers, we obtain an AR for exposed persons of 213/330=0.65 or 65%. That means, 65% of all accidents involving an intoxicated driver can be attributed to the effects of alcohol. However, in only 16.8% of all accidents (or 330 accidents) was the driver intoxicated. To determine which proportion of all accidents are attributable to the effects of alcohol, the population AR should be computed. This is done by dividing the excess accidents by the total number of all accidents, that is, 213/1968=0.108. Thus, 10.8% of all accidents may be attributed to the effects of alcohol. >>>
In other words, the most expert government data manipulation proved that 89.2% of the fatal accidents in this study were NOT caused by alcohol, but were caused by OTHER factors. In other words, the average driver in this study was 8.3 TIMES more likely to be killed in an accident where alcohol was NOT a factor than he was to be killed in an accident where alcohol WAS a factor?
WHAT are these other factors? Why is it assumed that these other factors which are responsible for 89.2% of the accidents are not the IDENTICAL factors involved in the fatal accidents which �may be attributed to the effects of alcohol�?
AND THIS IS *AFTER* MAKING THE FOLLOWING EGREGIOUS METHODOLOGICAL ERRORS
Had this subset of 1,968 German drivers who were involved in 4,681 accidents been a randomly selected subset of all 6,981 drivers who were involved in these accidents, this might have been an acceptable statistical analysis. But to compound the error, they admitted that this subset was not randomly selected. The subset included only the German drivers who the police themselves, not courts, and not the drivers, determined were "responsible" for the accident. Note the wording "responsible", and ask yourself how 5,013 or 71.8% of these German drivers could not have been "responsible" for an accident they were in. To compound the error even further, they made the presumption that all drivers who had a bac > 0 were "responsible" for the accident, while 71.8% of the drivers were not. This is great advocacy, but it's terrible science. It's worse than "guilty unless you prove your innocence", because drivers who were never even proven to have been "responsible" for the accident, who never even had a chance to present their case to a court of justice, were used as an excuse to terrorize German drivers all around Germany.
In other words, they started with a faulty premise, and when the data didn't support that premise, they changed the statistical rules to make the data fit the faulty premise. If you think drinking drivers are the criminals--then you don't understand how serious the problems are that scientists like this have caused to societies all around the world.
If you've followed this so far, at least you now know why they wanted to compare the Roadside Survey against only a subset of the accident data--it made the drinking driver appear to be involved in 3 1/2 times as accidents as he was. By comparison, police reports of American accidents show that only 4% are "alcohol involved". There are several reasons that this report may have concluded that .7% more German than American accidents are "alcohol involved":
The conclusions of this report would have been drastically different had the statistical analysis been done properly. Where it appears that drinking drivers were only 5.5% of all drivers, but were 7.2% of all drivers involved in accidents (suggesting that alcohol was a factor in those accidents), we now know that drinking drivers are 6.7% of all the drivers, but are involved in only 4.7% of all of the accidents. Where the odds ratio favored nondrinking drivers as 34.4% less likely than the drinking driver to have an accident, the odds ratio now favors the drinking driver to be 45.7% less likely than nondrinking drivers to have an accident. Let's put this another way. The procedure used by the German statisticians "disclosed" that drinking drivers as a group were 32.7% more likely than nondrinking drivers as a group to have an accident, whereas the correct procedure would have shown that nondrinking drivers as a group are 45.7% more likely than the drinking drivers as a group to have an accident.
Why did these government sponsored researchers resort to such a skewed approach?
Original Critique of German DUI Study April 4, 2006
This study of 4,615 accidents examining the effects of drinking and driving in Germany, where speeds over 140 mph on the autobahns are common, has all the earmarks of a bureaucrat trying to justify his position. But it contains much useful data, particularly considering that we have 45.8% more traffic fatalities per 100,000 population than Germany. 1,968 drivers were determined to have been responsible for some portion of these accidents, and 330 drivers, or 7.2% of them, had a BAC greater than 0.01%. This group was compared against a Roadside Survey of 9,269 Germans in Bavaria who were stopped at random and analyzed for their blood alcohol content, and it was reported that 510 of them (representing 5.5% of all German drivers) have a BAC greater than 0.01%.
But--5.2% or 501 of them refused the test.
Now. Stop right there. This study proceeds as if though only 5.5% of German drivers (in a country which consumes 50% more alcohol per capita than Americans) have a BAC greater than 0.01%, which by itself should sound all kinds of alarms. But the fact that the study ignored the *reason* that most of the 5.2% of them refused the test, namely that they had been drinking and did not want police with guns who stopped them at random in the middle of the night to know that, completely invalidates this control group. No data derived from such a grievous manipulation of the facts can be trusted from this point forward, no matter how well done the study may be.
ARE DRINKING DRIVERS 32% MORE DANGEROUS THAN NONDRINKING DRIVERS?
If only 5.5% of all German drivers are drinking drivers [read: have a BAC > 0 at any one time], but 7.15% of them are involved in accidents, then we concede that nondrinking [read: those with a BAC = 0] drivers are 24.4% less likely to have an accident than drinking drivers.
BUT: IT COULD BE THAT NONDRINKING DRIVERS 55% MORE DANGEROUS THAN DRINKING DRIVERS
If 10.7% of all German drivers have a bac > 0, and only 7.15% of them are involved in accidents, then the nondrinking drivers are 55.6% MORE likely to have an accident than drinking drivers. Why did this study ignore this point? And why is this significant? Well, it invalidates the entire premise of the study, namely that drinking drivers are more dangerous than non-drinking drivers. The authors didn't want you to know that because it was funded by the German government who wants to crack down on drinking drivers, and it's difficult to justify the draconian measures they have in mind if they're cracking down on the wrong group. Germans are very good at paying attention to detail, which is why it's surprising that they would permit a "detail" which would have completely reversed their conclusions to slip by.
If the original faulty premise doesn't reflect on the rest of the study, then it does contain some other interesting facts. Let's get equally as sloppy as the authors and proceed with the assumption that 100% of those who refused this DWI test had been drinking alcohol, which would mean that 10.7% of the drivers in the control group had a bac greater than 0.01. Let's assume that they are representative of all German drivers--that 10.7% of German drivers have a bac greater than 0.01% at any one time. Their discovery that drivers with a bac between 0.01 and 0.06 have a safer driving record than drivers with a bac of zero and that "heavy drinkers" and "excess drinkers" who adjust to drinking and driving improve their safety record quite a bit are points that cannot be ignored, particularly if the amount by which drivers with a bac between 0.01 and 0.06 are safer than drivers with a bac = 0 is greater than the amount by which drivers with a bac of .12 are more dangerous than drivers with a bac between 0.01 and 0.06. If you want to crack down on drivers with a bac = .12, you must also crack down on drivers with a bac = 0. After all, it would be "discrimination" to ignore them.
NONDRINKING DRIVERS 43% MORE DANGEROUS THAN 'THE GOLD STANDARD'
Can you even imagine the irony that the German government funded this study because it wanted to prove that drinking and driving causes accidents, but instead confirmed numerous other studies (i.e., the "Grand Rapid Study", and a study of airline pilots) that nondrinkers have 43% more accidents than moderate drinkers with a bac = .04%? What kind of government policy should be derived from such a revelation, especially since "liberals" believe that "if it costs a trillion dollars just to save one life, then it's worth it"? The difference is not small. It shows that if all nondrinking drivers had a propensity to have accidents that was equivalent to drivers with a bac = .04, that they would have 30% fewer accidents. Needless to say, this report doesn't make this point directly, but anyone who reads it can easily determine this.
Why should sober drivers be permitted to drive around having 95% of all the accidents just because they're 43% more likely than moderate drinkers to have accidents? Should they be outlawed, driven out of town on a rail, and tarred and feathered? Should yellow arm bands be wrapped around their tail pipes? Should they all be required to wear Dewey Buttons?
The least we can do is award drivers with a bac = .04% (those who have proven time and time again, around the world, in numerous studies of various hand/eye coordination tasks, that they have 30% fewer accidents than those with a bac = 0) a title. Let's award them the title of the "Gold Standard". If all drivers and pilots had their safety record, the lives saved would be worth far more than gold.
HOW TO SAVE 12,450 LIVES PER YEAR WITH 'THE GOLD STANDARD'
Consistent with the pattern discovered in the US, this report revealed two significant dips in the curve, one with a bac = .12% and another with a bac =.20%. These dips were so large that drivers who had these two bac levels were not that much more likely to have an accident than women drivers with a bac = 0. It pales in comparison to how much more dangerous the sober driver in this study was than the Gold Standard, mainly because there were 6,651 nondrinking drivers who were 43% more likely than the Gold Standard to have an accident, whereas there were only 18 drivers with a bac = .12% and only 28 drivers with a bac = .20%.
What would the perfect totalitarian state be thinking right now? With citizens having already accepted the notion that the state should monitor our bodily fluids to attempt to predict beforehand who will and who will not have an accident, it's not that much of a stretch to simply equip every car with an intravenous system which maintains our blood alcohol content at precisely .04%. After all, human life is at stake here, and intravenous systems are cheap. A 30% reduction in our traffic fatality rate would save 12,450 American lives per year. This is not a serious proposal.
PLAYING THE DEVIL'S ADVOCATE!
If the distribution of bac of German drivers who refused the test was equivalent to drivers who did take it, then the Gold Standard (the driver with a bac = .04%), rather than being only 30% less likely to have an accident than the sober driver, would now be two thirds less likely, or one third as likely, to have an accident. Where it would have been estimated that there should have been 59 drivers with a bac = .04 involved in these accidents, there were actually only 21 (64% fewer). Where there should have been 107 with a bac = .02, there were actually only 53 (50% fewer). Where there should have been 24 with a bac = .06, there were actually only 13 (46% fewer).
Even though this and other flaws render the study completely and totally worthless to setting social policy, the data is more revealing of what goes on behind the scene of governments than most of that produced in the US. The mere fact that they insisted that they don't even know with certainty whether or not 5.5%, or 10.7%, of German drivers have a bac > 0 at any one time is very sloppy scholarship for Germans, which illustrates how strict their orders are to NOT release the actual data. Of course they know exactly what these figures are but just don't want the taxpayer asking too many questions.
The creative way they got the word out that nondrinking drivers are 43% more likely than The Gold Standard to have an accident confirms an otherwise inexplicable feature of the NHTSA data: that nondrinking drivers are more dangerous than drinking drivers. This isn't necessarily because they have a higher accident rate than drivers with a bac > .20, but because there are 25 times as many of them. Of the 1,638 nondrinking drivers who were at fault for some portion of these 4,615 accidents, 491 of them would not have had an accident if they had had an accident rate equivalent to The Gold Standard. This is more than twice as many drivers as this study claims had an accident because of alcohol, using even their most liberal assumptions. If all the nondrinking drivers in this study had had a safety record equivalent to The Gold Standard, the overall accident rate in this sample would have been 10.6% lower and the number of drivers causing accidents would have been 25% lower.
NON-DRINKING GROUP IS FAR MORE DANGEROUS THAN THE DRINKING GROUP
Which is a conclusion which is contrary to their assigned task. Their task was to justify bigger government--not to seek truth and justice. The two are usually mutually exclusive of each other.
Study Completed Invalidated if only ONE THIRD of those Who Refused to be Tested Would Have Tested Positive
If we assume that the text in the study is correct, and that the actual data reported in the table is wrong, then the difference between the percent of all drivers with a positive BAC (5.5%) and the percent of drivers in fatal accidents (7.2%) is a mere 1.7%. This would not be so bad if this study had actually obeyed simple statistical methodologies--except that we have no idea what percent of the 501 or 5.2% of them who refused the test in the roadside study would have tested positive. If only a third of them would have tested positive had they not refused to be tested (a completely reasonable and probable assumption), then there would have been a higher percentage of drivers who tested positive in the roadside study than who tested positive in fatal accidents (7.3% vs. 7.2%, or 677 drivers in the roadside study versus 503 drivers in fatal accidents). THIS alone would have meant that the odds of a non-drinking driver having an accident, no matter how slight, is GREATER than the odds of a drinking driver having one.
SUMMARY OF THE DATA
3.1% of German drivers in accidents had a BAC greater than 0.10, compared to 62 or 0.67% of roadside study drivers who are KNOWN to have had a BAC that high, plus an undetermined number of the 501 who refused to take the test, raising this to a minimum of 229 or 2.5% to a maximum of 563 or 6.2%. In the LATTER case, IF 6.2% of all drivers have a BAC greater than 0.10 and only 3.1% of them are involved in fatal accidents, then their relative risk is 50%, and the relative risk of sober drivers is POSITIVE.
WHAT ABOUT WOMEN DRIVERS?
What about women drivers? It's well established, and even acknowledged on the FARS web site, that women drivers at any BAC level are "more than 50% more likely" than men drivers to have an accident. But compared to the Gold Standard who are 30% less likely to have an accident than the group of men drivers to whom women drivers are compared, the difference changes drastically, to 143%. In other words, the ordinary woman driver is 2.4 times more of a danger to society than the Gold Standard. What about women drivers who drive 30% of the miles in this country, who are 2.4 times more likely to have an accident than the Gold Standard, and who increase the risk of an accident for all drivers, including the Gold Standard?
"The analysis by Connolly,
Kimball, and Moulton (1989) mentioned above suggests that
female drivers have both a higher overall crash risk and a higher
alcohol-related fatal-crash risk. Combined data from FARS and the 1986 National
Roadside Breathtesting Survey suggest that the relative fatal-crash risk of a
female driver with a BAC of 0.10% or more could be of the order of 50% higher
than it is for a male driver at the same BAC. Of course, estimates based on
these two unmatched data sets are, as indicated above, are only very rough, but
they are consistent with prior case-control studies (see Jones and Joscelyn
Connolly, MA; Kimball, AW; and Moulton, LH. (1989). Alcohol and traffic safety: a sensitivity analysis of data from composite sources. Accident Analysis and Prevention 21(1):1-31.
HV 675 A1 A3
Risk factors of fatality in motor vehicle traffic accidents, Akira Shibataa
and Katsuhiro Fukudaa, Department of Public Health, Kurume University School of
Medicine, 67 Asahi-machi, Kurume, Fukuoka, 830, Japan "
Risk factors of fatality in motor vehicle traffic accidents, Akira Shibataa
and Katsuhiro Fukudaa, Department of Public Health, Kurume University School of
Medicine, 67 Asahi-machi, Kurume, Fukuoka, 830, Japan
However, per mile driven, women truckers are as much as 4 times as likely as men truckers to have an accident, and per hour flown, women pilots are four times likely as men pilots to have an accident. A detailed analysis of the FARS data base confirms that "could be of the order of 50% higher than it is for a male driver" actually means four times as likely for women drivers in general as well.
If women drivers are only 50% more likely than men drivers to have an accident and constitute half of all drivers
x + y = 213
x + 1.5x = 213
2.5x = 213
X = 85
Y = 128
128 or 60% of the 213 excess drivers on the above table are women and 85 are men who constitute a total of 4.3% the 1,968 drivers in fatal accidents in this study
If women drivers are twice as likely to have accident than men drivers and constitute half of all drivers
x + y = 213
x + 2x = 213
3x = 213
X = 71
Y = 142
142 or two thirds of the 213 excess drivers on the above table are women and 71 are men who constitute a total of 3.6% the 1,968 drivers in fatal accidents in this study
Black Drivers on American Highways Mostly Absent from German Autobahns
A United Nations study found that African cars are 145 TIMES as dangerous as Swiss cars and that cars in the Central African Republic are 2,472 times as dangerous as cars in Malta. Thus American black drivers are the most likely reason American cars on average are two to three times more dangerous than most European cars in spite of all our expansive, expensive, intrusive, unconstitutional, and FAILED government interventions. Regardless of just how much drinking and driving MIGHT impair his driving, it's disingenuous to the max to attempt to use a study in Germany where there there are few blacks to denigrate, castigate, and criminalize the White driver who clearly has the SAFEST driving record in the world, both here and in Europe (and undoubtedly in Africa).
If American blacks are only 100 times as dangerous on the road as American Whites and if they constitute a mere 4% of the drivers, then they are responsible for 81% of all fatal accidents. However, if they constitute as much as 10% of all drivers, a serious possibility, then they constitute 92% of all fatal accidents. There's little reason to believe that American blacks who are mostly hybrids would perform any better in any field than their pure bred Black cousins back in Africa, particularly in light of the Beaton Gonzalez correlation study which shows that the most coddled Blacks in the world, the highest paid and most subsidized and financially protected in DC, are neck to neck with dirt poor blacks in Mozambique in international math scores like IAEP (217 vs. 224, compared to 294 for Korea and 281 for North Dakota). It's entirely possible that they drive just as dangerously as their cousins back in Africa, which means they are 1,000 times as likely to have an accident, which means that they would constitute 99% of all fatal accidents.
This might not seem plausible given the lack of news coverage of this roadside slaughter of Americans, but consider just how little media coverage there has been for the FBI Uniform Crime Report which estimates that 51% of all homicides in the country are committed by the 1% of the American population who are Black male youths between the age of 14 to 24.
Grand Rapids Effects Revisited: Accidents, Alcohol and Risk
H.-P. Kr�ger, J. Kazenwadel and M. Vollrath
Center for Traffic Sciences, University of Wuerzburg, R�ntgenring 11, D-97070 W�rzburg, Germany
Risk analysis is based on information collected about both exposure to danger and the dangerous event itself. In the case of alcohol-related accident risk, information is needed about the prevalence of driving under the influence of alcohol (DUI) and the frequency with which DUI drivers are involved in accidents. These requirements were met in Borkenstein et al.'s Grand Rapids Study. However, one shortcoming of that study was the risk of causing an accident (rather than just being involved in an accident) had to be estimated because the authors did not know whether the driver was responsible for the accident. Our 1993 Accident Study collected information about BAC, responsibility for causing the accident, and driver characteristics for all drivers involved in 4,615 accidents. The information about exposure was taken from the German Roadside Survey, which sampled 13,149 drivers in 1993. Using those data, the well-known risk function of Borkenstein et al. was replicated. However, the BAC distribution for drivers involved in an accident but not responsible for it was markedly different from that for the drivers in the Roadside Survey. In calculating risk function, Borkenstein et al. assumed identical distributions for these two samples. It can be shown that the problematic "dip" in the risk function was at least in part caused by this assumption.
Risk analysis is based on information collected about both exposure to danger and the dangerous event itself. In the case of alcohol-related accident risk, information is needed about the prevalence of driving under the influence of alcohol (DUI) and the frequency with which DUI drivers are involved in accidents. Although these requirements were met in Borkenstein et al.'s Grand Rapids Study the study has one shortcoming: The risk of causing an accident (rather than just being involved in one) had to be estimated because the authors did not have information on whether the driver was responsible for the accident. In our Accident Study, which took place in Germany in 1994, we obtained this information directly from the police. All the analyses described below include only those drivers who were responsible for causing the accident. Information about DUI prevalence was obtained from the German Roadside Survey (see Kr�ger et al., 1995, in this volume). The risk function resulting from our 1994 study is, in general, comparable to that resulting from the Grand Rapids Study. However, important differences were found concerning the steepness of the risk functions. In addition, it is demonstrated that the global risk function has to be differentiated for subgroups of drinking drivers. The impact of measures directed against these drivers is estimated by means of the attributable risk.
The German Roadside Survey was conducted in the northern part of Bavaria (Unterfranken, part of the former West Germany), which has approximately 3 million inhabitants. Three components were done from the end of 1992 to the spring of 1994. Drivers were stopped and selected by the police who followed a random sampling plan. At a separate checkpoint, these drivers were interviewed and asked to supply a breath sample. Of those asked for a breath sample, 9128 (94.8%) agreed. The roadside survey oversampled weekends at night to obtain a large proportion of DUI drivers. For a representative picture of the DUI prevalence in Germany, the observations were adjusted using information from a representative study of driving in Germany (KONTIV; see Emnid, 1991).
The Accident Study was also conducted in Unterfranken. We equipped a selected sample of police cars with breath testing devices, under the condition that officers try to obtain breath samples from all accident drivers, whether or not they were suspected of DUI. In 1993 in Unterfranken, data were obtained from 1.968 drivers who were responsible for causing an accident.
The Roadside Survey and the Accident Study differed very much with regard to time of day (night: 20 p.m. to 4 a.m.; day: 4 a.m. to 20 p.m.) and day of week (weekend: Friday night to Monday morning; workday: Monday morning to Friday evening). These differences are reflective of such risk factors as, for example, the higher accident risk during the night. As we were mainly interested in alcohol-related accident risk, we controlled for these variables by applying a second weighting procedure to the data from the Roadside Survey. This two-dimensional weighting (by time of day and day of week) produced identical subject distributions in the two studies with respect to the combination of those two factors.
The alcohol-related accident risk is estimated by computing odds ratios. An odds ratio gives a good estimation of the relative accident risk for drivers in a certain BAC class compared to sober drivers (their risk is set to 1). A value larger than 1 indicates an increase in accident risk due to alcohol.
Risk Functions in 1964 and 1994
In 1964, Borkenstein et al. presented the well-known risk function for drivers responsible for causing an accident, which was one basic argument for setting BAC limits in different countries (for example, Germany). Figure 1 shows this risk function compared with the function computed from the Accident Study (both functions were smoothed). The shape as well as the magnitude of the functions are very similar. For drivers with blood alcohol concentrations (BAC) up to 0.04%, the alcohol-related accident risk is nearly identical to or even less than that for sober drivers. Both studies found that, for drivers at BACs ranging from 0.14% to 0.16%, the accident risk is about 25 times as high as it is for sober drivers. However, for nearly all BACs, the 1994 alcohol-related accident risk in Germany was greater than in 1964, a finding that may be a function of today's more complex traffic situations, which in combination with alcohol cannot be handled adequately anymore. At BACs greater than 0.14%, the deteriorating effects of the intoxication may be so great as to make the differences in traffic conditions irrelevant.
Analysis of factors modifying the alcohol-related accident risk showed driver age to be the strongest mediator (see Vollrath, Kr�ger & Kazenwadel, 1994; Kr�ger, Kazenwadel & Vollrath, 1995). The global accident risk for drivers between 18 and 24 years is much greater than that for older drivers. In addition, the alcohol-related accident risk for those young drivers increases much faster than it does for older drivers. In light of these findings, we strongly recommend lowering the BAC limit for younger drivers.
The Attributable Risk
Although drivers under the influence of alcohol are obviously at a greater relative risk than unintoxicated drivers, the magnitude of the risk to the larger community attributable to the presence of intoxicated drivers remains an unanswered question. In the German Roadside Survey, only 5.5% of all drivers were found to have BACs greater than 0. Thus, drivers in Germany are exposed to the increased accident risk due to DUI in only 5.5% of their trips (this statement is valid because of the representative weighting procedure described above). By combining the information about the distribution of exposure (DUI) with the estimate of alcohol-related accident risk, one can determine the degree to which accidents can be explained by DUI. This question is adressed by the measure of the attributable risk (for an overview, see Breslow & Day, 1980; Kahn & Sempos, 1989). The basic idea of attributable risk is that some of the accidents involving intoxicated drivers are not due to the effects of alcohol but are the result of the global accident risk also present for sober drivers. This means that the number of accidents involving intoxicated drivers is adjusted to allow for this global accident risk, yielding an excess number of accidents which are attributable to the effects of alcohol.
There are two definitions of attributable risk (AR), addressing two different aspects: (1) The attributable risk for exposed persons (Cole & MacMahon, 1971) renders an estimate of the proportion of all accidents with intoxicated drivers that is attributable to the effects of alcohol. (2) The attributable risk for the population (first described by Levin, 1953) renders an estimate of the proportion of all accidents (including those with sober drivers) that is due to the effects of alcohol.
To compute these ARs, we chose the BAC classes given in Table 1. The first column shows the number of drivers from the German Roadside Survey according to BAC class, and the second column the number of drivers from the accident study. The first step in computing the number of accident-involved drivers within each BAC class attributable to the effects of alcohol (excess) is to compute a factor k of accident involvement for sober drivers. This factor is calculated as:
Using this factor, the number of drivers that would be expected to be responsible for causing an accident is estimated for each BAC class. For example, for a BAC greater than 0.20%, 10 drivers were found in the Roadside Survey. Multiplying this number by k results in 10 * 0.1941 = 2. Thus, we would expect 2 drivers to be found in the Accident Study in this BAC class (not due to alcohol). However, 64 were found yielding an excess number of 62 accidents which may be attributed to the effect of alcohol. Those excess numbers are given in the third column of Table 1. Of course, there are large difference among the BAC classes. At lower BACs, we even find negative numbers indicating the "dip" in the risk function for lower BACs first described by Borkenstein et al. (1964).
For all BAC classes above 0%, we found 330 drivers in the accident study. Of those accidents, 213 were attributable to the effects of alcohol. By dividing those two numbers, we obtain an AR for exposed persons of 213/330=0.65 or 65%. That means, 65% of all accidents involving an intoxicated driver can be attributed to the effects of alcohol. However, in only 16.8% of all accidents (or 330 accidents) was the driver intoxicated. To determine which proportion of all accidents are attributable to the effects of alcohol, the population AR should be computed. This is done by dividing the excess accidents by the total number of all accidents, that is, 213/1968=0.108. Thus, 10.8% of all accidents may be attributed to the effects of alcohol.
Figure 2 gives both ARs computed for different BAC classes. The AR of exposed drivers indicates for each BAC class the percentage of accidents attributable to alcohol. For BACs less than 0.06%, the AR is small, even negative. Hardly any accidents involving drivers with those BACs can be attributed to intoxication. This changes dramatically for BACs greater than 0.06%. At BACs less than 0.08% but greater than 0.06%, about 70% of all accidents are due to alcohol. For all BAC classes greater than 0.08%, the ARs are greater than 80%. For drivers in this latter BAC categories, nearly all the accidents may be attributed to the effects of alcohol.
The AR of the population indicates the magnitude of those alcohol effects in relationship to the total number of accidents occuring. The population ARs can be interpreted as follows: If no drivers with BACs greater than 0.20% were present in traffic, 3% of all accidents would not happen. Adding these percentages for all BAC classes gives the 10.8% of all accidents which are due to alcohol. About a third of these accidents can be attributed to drivers with BACs greater than 0.2%.
As Figure 3 shows, this population AR gives a good indication of the effectiveness of measures directed against DUI. In this Figure, the 10.8% accidents were set to 100%. Had no DUI drivers been present in traffic, none of these accidents would have occured, which would have resulted in a 100% reduction. If no one with a BAC greater than 0.08% drove, a reduction of 96% would result. Thus, if the legal limit for DUI in Germany (0.08%) was an effective deterrant against driving with a higher BAC, this would mean that nearly everything that could be done to prevent alcohol-related accidents would have been accomplished. Thus, countermeasures directed at those persons driving at BACs higher than 0.08% can be expected to be most effective in reducing the number of accidents attributable to the effects of alcohol. In contrast, measures directed at drivers with BACs less than 0.08% cannot be very effective. At most, 4% of all accidents attributable to the effects of alcohol may be prevented.
Sub-Groups Included in the Risk Function
The question remains how to indentify the characteristics of the these drivers with BACs greater than 0.08%. Is driving with high BACs done very seldom by nearly all drivers or is it done quite often by a small subgroup of drivers? We can begin to answer this question be analyzing the risk functions in Figure 1 in detail. These smoothed functions give the impression that alcohol-related accident risk increases monotonically. However, if smaller BAC classes are selected and BAC is truncated at 0.18%, the picture changes. In Figure 4, odds ratios were computed for BAC classes of 0.02%. The risk functions are shown from our Accident study, from the Grand Rapids Study (drivers responsible for the accident), and from a study by Perrine, Waller & Harris (1971) of fatally injured drivers.
Although the studies were done at different times in different countries, the similarities in the structures are striking. In none of the three risk functions is there a monotone increase in risk, but different peaks are found. In our Accident study, the first (small) peak is present between 0.08% and 0.10%, a second peak at 0.14% to 0.16% and a third peak at BACs greater than 0.20%. In the Grand Rapids Study, similar peaks are found but are shifted towards higher BACs. This reflects the finding shown in Figure 1 that, in our Accident Study, the alcohol-related accident risk is higher than that found by Borkenstein et al. (1964). In contrast, in Perrine et al.'s study, the peaks are shifted towards lower BACs, which makes sense as only fatally injured drivers (very serious accidents yielding a larger alcohol-related accident risk) were examined.
The occurence of those peaks in three different studies from different countries and different years suggests that the overlay of risk functions of different sub-populations produces the typical shape of the overall risk function. Extended studies on drinking behavior indicate that three different groups of drinkers may be responsible for the peaks. These hypothesis is supported by studies on hardcore drinking drivers (for example, Simpson & Mayhew, 1993). The assumption of three sub-groups of drinkers is indicated in Figure 5 (the risk function here was computed from our data for BAC classes of 0.01%). The first group consists of moderate drinkers who will never exceed a maximum BAC of around 0.10% (consumption limit). At higher BACs, this group cannot compensate the effects of alcohol very well, which yields the first peak of the risk funktion. Two groups of heavy drinkers are responsible for the other peaks. Both groups have probably developed a certain amount of alcohol tolerance, enabling them to compensate for the effects of alcohol at higher BACs.
Our Accident Study replicated the well-known risk function of Borkenstein et al. (1964). The comparison indicates that driving under the influence of alcohol resulted in a greater accident risk in 1994 compared to 1964. Considering the incidence of DUI, it was argued that effective countermeasures that substantially reduce the number of accidents attributable to the effects of alcohol should be directed towards drivers with BACs greater than 0.08%. This also implies that simply changing the legal DUI limit from 0.08% to 0.05% is insufficient with respect to alcohol-induced accidents as the potential reduction would be only about 4%. Further inspection of the risk function indicates that certain subgroups of drinking drivers are responsible for the alcohol-related accident risk in the higher BAC range. Measures capable of deterring drinking drivers in this range were expected to have a substantial impact on traffic safety, namely, result in a decrease in accident rates.
Borkenstein, R.F., Crowther, F.R., Shumate, R.P., Ziel, W.B. & Zylman, R. (1964). The role of the drinking driver in traffic accidents. Department of Police Administration, Indiana University.
Borkenstein, R.F., Crowther, F.R., Shumate, R.P., Ziel, W.B. & Zylman, R. (1974). The role of the drinking driver in traffic accidents (The Grand Rapids Study). Blutalkohol, 11, Supplement 1.
Breslow, N.E. & Day, N.E. (1980). Statistical methods in cancer Research. Volume 1 - The analysis of case-control studies. Lyon: International Agency for Research on Cancer.
Cole, P. & MacMahon, B. (1971). Attributable risk percent in case-control studies. British Journal of of Prevention and Social Medicine, 25, 242-244.
Emnid (1991). KONTIV 89. Bericht zur Methode, Anlagenband und Tabellenteil. Bielfeld: Emnid.
Kahn, H.A. & Sempos, C.T. (1989). Statistical methods in epidemiology. New York: Oxford University Press.
Kr�ger, H.-P., Kazenwadel, J. & Vollrath, M. (1995). Das Unfallrisiko unter Alkohol unter besonderer Ber�cksichtigung risikoerh�hender Faktoren. In H.-P. Kr�ger (Hrsg.), Das Unfallrisiko unter Alkohol. Stuttgart: Fischer Verlag (in preparation).
Levin, M.L. (1953). The occurrence of lung cancer in man. Acta Unio Internationale Contra Cancrum, 9, 531-541.
Simpson, H.M. & Mayhew, D.R. (1993). The hard core drinking driver. In H.-D. Utzelmann, G. Berghaus & G. Kroj (Eds.), Alcohol, Drugs and Traffic Safety - T92 (pp. 847 - 853). Cologne: T�V Rheinland.
Vollrath, M., Kr�ger, H.-P. & Kazenwadel, J. (1994). Modifying risks: Youthful drivers, drinking drivers and driving conditions. 1994 Annual Scientific Meeting of the Research Society on Alcoholism (RSA), Maui.