Global burden of injuries attributable to alcohol consumption in 2004: a novel way of calculating the burden of injuries attributable to alcohol consumption

Background Alcohol consumption is a major risk factor for injuries; however, international data on this burden are limited. This article presents new methods to quantify the burden of injuries attributable to alcohol consumption and quantifies the number of deaths, potential years of life lost (PYLL), and disability-adjusted life years (DALYs) lost from injuries attributable to alcohol consumption for 2004. Methods Data on drinking indicators were obtained from the Comparative Risk Assessment study. Data on mortality, PYLL, and DALYs for injuries were obtained from the World Health Organization. Alcohol-attributable fractions were calculated based on a new risk modeling methodology, which accounts for average and heavy drinking occasions. 95% confidence intervals (CIs) were calculated using a Monte Carlo simulation method. Results In 2004, 851,900 (95% CI: 419,400 to 1,282,500) deaths, 19,051,000 (95% CI: 9,767,000 to 28,243,000) PYLL, and 21,688,000 (95% CI: 11,097,000 to 32,385,000) DALYs for people 15 years and older were due to injuries attributable to alcohol consumption. With respect to the total number of deaths, harms to others were responsible for 15.1% of alcohol-attributable injury deaths, 14.5% of alcohol-attributable injury PYLL, and 11.35% of alcohol-attributable injury DALYs. The overall burden of injuries attributable to alcohol consumption corresponds to 17.3% of all injury deaths, 16.7% of all PYLL, and 13.6% of all DALYs caused by injuries, or 1.4% of all deaths, 2.0% of all PYLL, and 1.4% of all DALYs in 2004. Conclusions The novel methodology described in this article to calculate the burden of injuries attributable to alcohol consumption improves on previous methodology by more accurately calculating the burden of injuries attributable to one’s own drinking, and for the first time, calculates the burden of injuries attributable to the alcohol consumption of others. The burden of injuries attributable to alcohol consumption is large and is entirely avoidable, and policies and strategies to reduce it are recommended.


Introduction
Alcohol consumption is the sixth leading cause of death and the third leading cause of disability-adjusted life years (DALYs) lost globally, with injuries accounting for a large part of the alcohol-attributable burden of disease [1,2]. Previous research, with varying study designs such as crosssectional studies [3], case-crossover studies [4], case-control studies [5], systematic reviews, and meta-analyses [6,7] has shown a strong association between alcohol consumption and many types of intentional and unintentional injuries. Moreover, it has been shown that alcohol consumption fulfills the standard epidemiological criteria of causality for many injury outcomes [8]. However, reporting of the burden of injuries has not kept pace with new methodology to calculate alcohol-attributable risk. Previous global estimates of the alcohol-attributable burden of injuries were calculated using simplistic methods based on one country and then scaling these estimates according to average volume of consumption and patterns of drinking [9]. The most recently proposed method of calculating the alcohol-attributable burden of disease did not account for injuries caused by other people's drinking (the burden of which has been estimated to be substantial [10,11]) or account for the overlap in binge consumption and average consumption, which leads to an overestimation of the alcohol-attributable injuries caused to the drinker [12].
In this article we present new methodology to calculate the alcohol-attributable burden of disease for injuries using formulas that take into consideration the main drivers of alcohol-attributable risknamely average daily consumption and binge drinking. This calculation of the global burden of injuries attributable to alcohol is possibly due, in part, to the persistent relationship between alcohol consumption and injury risk which has remained strikingly similar throughout the last 50 years of observational research [13,14] and across cultural and geographical boundaries [15][16][17][18]. This means that, although drinking patterns may vary across countries, cultures, and age and sex groups, the same risk function can be used for all countries to determine injury burden estimates based on country-specific drinking behavior. This information can be aggregated to regional or global levels to gain a more accurate comparative picture.
It is the aim of this article to utilize the new methodology outlined herein to estimate the burden of alcoholattributable injuries caused to the drinker and to others, and to estimate for 2004 the global burden of injuries attributable to alcohol consumption in terms of mortality, potential years of life lost (PYLL), and DALYs for each Global Burden of Disease (GBD) region.

Definition of regions and population data
The GBD regions (2005) are based on geography, child and adult mortality, and major causes of death [19]. Population estimates by country in 2004 were based on data obtained from the 2008 revisions of the United Nations Population Division [20].
Step 1: Calculation of the AAFs by sex and alcohol consumption Alcohol consumption measures Two dimensions of alcohol consumption play a role in affecting the probability of injury: binge drinking and average daily alcohol consumption.
the past month, assuming that the average drink size is 12 g of pure ethanol. Estimates for the prevalence of binge drinkers, current drinkers, and past year abstainers were obtained from the 2005 Comparative Risk Assessment (CRA) study [19]. Average daily alcohol consumption was calculated based on 80% of per capita consumption of alcohol (to account for alcohol not consumed) and the prevalence of current drinkers. Total adult (age 15 years and over) per capita alcohol consumption for 2004 for each region was calculated by adding the estimated recorded and unrecorded adult per capita consumption and then subtracting tourist (the amount of alcohol consumed by citizens of other countries) adult per capita consumption [21].
Estimates of recorded adult per capita alcohol consumption were obtained from the Global Information System on Alcohol and Health database [22]. These estimates were based on government records (taxation), industry publications for the production and sales of alcohol, and data from the Food and Agriculture Organization [22]. Unrecorded and tourist adult per capita consumption estimates were taken from the ongoing CRA study [22]. The main sources for unrecorded consumption were home production, alcohol intended for industrial, technical, and medical uses, and illegal production or importation of alcohol [22]. As no variance estimates for unrecorded and tourist alcohol consumption existed, we estimated the variance to be five times that of the variance of recorded alcohol consumption proportionate to the mean [23]. For this study we used two different types of drinking days: binge drinking days and average drinking days. Prevalence of binge drinkers and the frequency of binge drinking days and alcohol consumption on binge drinking days (for binge drinkers) were obtained from the 2005 CRA study. Average alcohol consumption on nonbinge drinking days (defined as a drinking day that was not a binge drinking day) was assumed to be the same for binge drinkers and nonbinge drinkers. Average alcohol consumption on nonbinge drinking days was calculated such that every day that a person was not binge drinking was considered to be an average drinking day. The volume of alcohol consumed on an average drinking day was then calculated using per capita consumption and binge drinking consumption, such that the amount of alcohol consumed on the nonbinge drinking days plus the amount of alcohol consumed on binge drinking days was equal to 80% of per capita alcohol consumption.

Risk relations
Sources for relative risk (RR) functions by GBD code are outlined in Table 1

Estimating the AAFs for harms caused to oneself
The AAFs for injuries were modeled according to methodology that takes into account two dimensions of alcohol consumption: 1 binge drinking (both the number of occasions and the amount consumed per occasion) 2 average daily alcohol consumption (on nonbinge drinking days) When calculating the AAFs, we also included alcohol metabolism rates for men and women to calculate a person's time at risk of an injury outcome, according to methods outlined by Taylor and colleagues [12].
The AAFs for intentional and unintentional injuries attributable to alcohol consumption were calculated as follows: AAF ¼ where P abs represents the prevalence of current abstainers, and P current(binge) and P current(non-binge) are the prevalence of current drinkers who engage in binge drinking and the prevalence of current drinkers who do not engage in binge drinking, respectively. The RRs were calculated separately for current drinkers who engage in binge drinking and current drinkers who do not engage in binge drinking. RR current(non-binge) was calculated as follows: RR currentðnonÀbingeÞ ¼ ðRR average À 1Þ Ã P nonbingedays þ 1 and RR current(binge) was calculated as follows: RR current binge ð Þ ¼ RR average À 1 À Á Ã P nonbingedays þ RR binge À 1 À Á Ã P bingedays þ 1 where risk on average drinking days (RR average ) was calculated as follows: RR average ¼ P dayatrisk x ð Þ Ã RR injury x ð Þ À À1Þ þ 1 and where risk on binge drinking days (RR binge ) was calculated as follows: x ð Þ À 1Þ þ 1 where P dayatrisk represents the proportion of a day at risk given an alcohol consumption on that day (x), and RR injury is the relative risk for injury given an amount of alcohol consumed (x), where x is the amount of alcohol consumed on binge drinking days for RR binge and the amount of alcohol consumed on nonbinge drinking days for RR average *P dayatrisk is calculated based on the average rate at which alcohol is metabolized.
Since these AAFs were calculated based on samples of emergency room patients, we estimated the AAF for mortality from motor vehicle accidents by multiplying the AAF for morbidity for motor vehicle accidents by 3/2. Similarly, to estimate the AAF for mortality due to nonmotor vehicle accidents, we multiplied the AAF for morbidity for nonmotor vehicle accidents by 9/4. These methods were based on two studies that compared blood alcohol levels of emergency room patients with blood alcohol levels obtained from coroners' reports of patients who died from an injury [24,25].
For women, the AAF for motor vehicle accidents was calculated by multiplying the AAF for motor vehicle accidents for men by the product of the per capita consumption of alcohol for women divided by the per capita consumption of alcohol for men.

Estimating the AAFs for harms caused to others
The AAFs for deaths and morbidity caused by drinkers to others due to motor vehicle accidents were calculated based on recent data reported by Laslett et al., 2011 [11]. The AAFs for the alcohol-attributable injuries to others were calculated as follows: AAF sefAustralia Þ where AAF Otherage represents the AAF for motor vehicle accident injuries caused by others, AAF selfcountryi represents the AAF for motor vehicle accident injuries caused to oneself for an entire country i, and AAF selfagecountryi represents the AAF for motor vehicle accident injuries caused to oneself for each specific age group. AAF selfAustralia represents the AAF for motor vehicle accident injuries caused to oneself in Australia, and AAF otherageAustralia represents the AAF for motor vehicle accident injuries caused by others for each specific age group in Australia.
The AAFs for deaths and injuries caused by an assault by someone who had been drinking were calculated based on recent data reported by Laslett et al., 2011. These AAFs were calculated as follows: where AAF Assaultage_countryi represents the age-specific AAF for deaths or injuries caused by assault, AAF Assault_countryi represents the AAF for assaults for an entire country, AAF Assault_Australia represents the AAF for deaths or injuries caused by assaults for Australia and AAF Assaultage_Australiai represents the AAF for deaths or injuries caused by assaults for each specific age group in Australia.
Estimating the 95% confidence intervals for the AAFs The 95% confidence intervals (CIs) for the AAFs were calculated using a Monte Carlo approach, with 40,000 simulations that estimated the lowest-level parameters used in the AAF formulas [23]. For the AAFs of binge and average consumption for each simulation, we generated estimates for the prevalence of past year abstainers from which a prevalence of current drinkers was estimated. Additionally, we generated estimates of the RR function betas and the formula used to calculate the average rate at which alcohol is metabolized, which, in turn, was used to calculate P dayatrisk . For the calculation of the 95% CIs, we also generated estimates for the prevalence of binge drinkers among current drinkers and the average number of drinks consumed on binge drinking occasions and on nonbinge drinking occasions. The resulting 40,000 AAF estimates for binge and average consumption were used to calculate the variance of the AAFs and the 95% CIs for each disease category.
Step 2: Application of the AAFs to region-specific mortality, PYLL, and DALY data This step required multiplying the sex-, age-, consumption-,and injury-specific AAFs by mortality, PYLL, and DALY data, respectively.

Estimates of mortality and morbidity
To quantify the burden of injuries attributable to alcohol consumption we used an event-based measure (mortality) and time-based measures (PYLL and DALYs). DALYs combine years of life lost due to premature mortality and years lived with disabilities. Comprehensive revision estimates for 2004 of mortality, PYLL, and DALYs for the 160 GBD disease and injury categories were provided by the World Health Organization (WHO) [26]. Methods to estimate the mortality, PYLL, and DALYs in the GBD project are described elsewhere [27,28]. Estimates of mortality, PYLL, and DALYs were available for each country, which were used to calculate regional estimates. This meant that for each region, sex-, age-, injury-, and consumption-specific AAFs were applied to sex-, age-, and injury-specific outcome data. All statistics and analyses were performed using R version 2.11.1. Table 2 outlines the prevalence of current drinkers, people who engage in binge drinking, average number of binge drinking days in a year, the average number of drinks consumed during a binge drinking occasion, and  per capita consumption by sex for each CRA region. Men exhibited a higher per capita consumption and a higher prevalence of current drinkers and of binge drinkers than did women in every region. The prevalence of current drinkers and per capita consumption varied greatly, with Western Europe having the highest prevalence of current drinkers and North Africa/Middle East having the lowest prevalence of current drinkers. Eastern Europe had the highest per capita consumption for men and women, while Southern Asia had the lowest per capita consumption for women and North Africa/Middle East had the lowest for men. Table 3 outlines the deaths attributable to alcohol consumption by region and sex. 851,900 (95% CI: 419,400 to 1,282,500) deaths were due to alcohol-attributable injuries, of which 221,100 (95% CI: 140,000 to 312,000) deaths were caused by alcohol-attributable harms to others (alcohol-attributable injuries caused by others are outlined in Additional file 1). Figures 1 and 2 outline the burden of injuries in deaths per 100,000 people for men and women, respectively. Alcohol-attributable injuries account for 1.43% (95% CI: 0.70% to 2.15%) of all deaths and 15.10% (95% CI: 7.43% to 22.73%) of all deaths from injuries. Of this total, 761,300 (95% CI: 390,800 to 1,088,900) deaths were among men, representing 2.42% (95% CI: 1.24% to 3.46%) of all deaths and 20.26% (95% CI: 10.40% to 28.98%) of all deaths from injuries for men. 90,600 (95% CI: 28,500 to 193,600) deaths were among women, representing 0.32% (95% CI: 0.10% to 0.69%) of all deaths and 4.81% (95% CI: 1.51% to 10.27%) of all deaths from injuries for women. Adjusting the figures in Table 3 for the population of each region, we observed that Eastern Europe had the largest population-standardized mortality rate, with 135.4 (95% CI: 82.0 to 161.4) deaths per 100,000 people caused by injuries attributable to alcohol consumption, and North Africa/Middle East had the lowest death rate, with 2.0 (95% CI: 0.5 to 5.5) deaths per 100,000 people caused by injuries attributable to alcohol consumption. All AAFs for injuries as well as alcohol-attributable injury deaths by age, sex, region, and cause are provided in Additional file 2, Additional file 3, Additional file 4 and Additional file 5.

Discussion
Alcohol is a substantial risk factor for the global burden of injuries in terms of death, PYLL, and DALYs. We found that this burden of injuries for 2004 varied by region corresponding with drinking prevalence: those regions exhibiting a low prevalence of current drinkers, such as in North Africa/Middle East and Southern Asia, carried a relatively low burden of injuries attributable to alcohol. This can be contrasted with Eastern Europe, where drinking prevalence, binge drinking, and the burden due to alcohol-attributable injury were all high. Before we discuss the implications of these findings, the potential weaknesses associated with this analysis should be discussed in detail. First, quantification of the global burden using insurance and police records, which would provide the most accurate data, appears not to be possible as no such reporting system exists [29]. Second, there are limitations regarding the quality of global mortality data (see [27]). For most of the world, there are no vital registries, i.e., there is scarce or no available information on causes of death. In these instances, data on the missing causes of death have to be statistically estimated [28,30,31]. Although we do not incorporate the variation of the mortality estimates in these countries into our analysis, estimations by the WHO/GBD of the number of deaths in countries where little or no data are available increase the uncertainty of our estimates of the number of deaths, PYLL, and DALYs attributable to alcohol consumption [27]. Third, there are weaknesses associated with the assumptions made in the calculation of the DALYs (see [32]), particularly the calculation of weights for DALYs, although these assumptions have been shown to exert only a minor effect on the variation of DALY estimates for injuries [27]. Fourth, alcohol consumption variables used in our analysis came from population surveys which have limitations with respect to coverage, and the survey instruments involved commonly have inherent biases due to self-reporting of data, leading to an underestimation of level of drinking and number of binge drinkers [33]. While the distribution of average volume of alcohol consumption can be adjusted for the amount of alcohol actually consumed [34], there is currently no methodology to correct the underestimation of irregular binge drinking [35], thereby causing an underestimation of the global burden of injuries attributable to alcohol consumption.
Our study is further limited by the use of the RR for all nonmotor vehicle accident injuries. We suspect that the risk relationship may change by injury type, but the body of research relating alcohol consumption to injury is relatively sparse (except with respect to motor vehicle accidents), meaning that meta-analytic techniques used to generate stable risk curves are not usable due to a scarcity of data points. This is especially important for alcohol consumption and resulting intentional and unintentional nonmotor vehicle accident injuries, due to alcohol playing a very different role in intentional and unintentional nonmotor vehicle accident injuries [6]. However, the risk estimates for intentional and unintentional injuries were not stable in the meta-analyses performed by Taylor and colleagues and, thus, were combined [6]. The resulting aggregate RR showed little heterogeneity among studies that examined intentional and unintentional nonmotor vehicle accident injuries [6]. Additionally, although not taken into consideration in our analysis, previous research has suggested that the RRs for injury may be dependent upon previous alcohol consumption patterns, with heavy consumers of alcohol at a lower risk than those people who do not frequently consume large amounts of alcohol [36][37][38].
Our study is limited also by the information on harms to others available in the literature; we used data from Australia to model harms to others. Because of limited data, we were unable to determine if a linear relationship exists between the AAFs for motor vehicle accident injuries to passengers, pedestrians, and drivers who did not cause the accident and the AAFs for motor vehicle accident deaths to drivers who caused the accident. We were also unable to quantify the relationship between age-specific AAFs for assaults and population AAFs for assaults. This lack of data leads to two different formulas being used for AAFs for motor vehicle accidents caused to others and for AAFs for assaults; the AAFs for assaults were calculated assuming a linear relationship, and the AAFs for motor vehicle accidents caused to others had to be log transformed. Log transformation of the AAFs for motor vehicle accidents caused to others was required in order to keep the resulting total AAFs within the boundaries of 0 and 1. In the case of the AAFs for assaults, log transformation was not necessary since the age-specific AAFs were very similar.
Regardless of these limitations, the method of calculating the burden of injury attributable to alcohol consumption presented in this article is an improvement on previous methods used to calculate the alcohol-attributable burden. For the first time at a global level the burden of alcohol-attributable injuries has been estimated using consumption data and RRs, and alcohol-related harms to others have been calculated.