Alcohol-Related Injuries: Evidence for the Prevention Paradox

Dr. Heller wonders if we used the correct formula for calculating a polytomous exposure's attributable risk. We've reread the article he cites by Hanley, checked with Dr. Heller, and confirmed that the calculations were correctly done. We greatly appreciate his thoroughness.

To calculate the PIN-ER-t for a particular community or practice, one would need to know the distribution of various patterns of drinking and the base rate of injury. Both of those can be learned, though it would take a bit of work. I hope others will take our results and find new ways to put them into practice, both in the work we do as family physicians and in public policies.

Dr. Nordstrom's quotation of the other version of the prevention paradox is quite appropriate. Like many of our preventive healthcare interventions (treating hyperlipidemia, for example), advising people to limit alcohol consumption to 1 drink per occasion would benefit each person who drinks 2 to 3 or 4 drinks only a little, but could prevent perhaps a million injuries in the U.S. each year.

The version of the prevention paradox that we cited in the paper, which is the version that has been the focus of previous papers looking at alcohol's risks, isn't confirmed by our study. Fewer than half of all alcohol-attributable injuries are attributable to light to moderate drinking. But the population attributable fraction is still sizable. Something for us all to ponder.

The lower limit of what is usually considered nonhazardous drinking is 1 drink. (Zero is also a nonhazardous amount, but that's beside the point here.) Dr. Nordstrom points to the last paragraph in our paper, "Consuming 2 or 3 alcoholic drinks for women, or 2 to 4 for men caused about 4% of all emergency department injury visits." Later in that paragraph, we note that those levels are "what has been considered a nonhazardous amount of alcohol." The point in that paragraph is not that the lower limit of nonhazardous drinking is 2 drinks instead of 1, but that 2 drinks has been considered (for most people most of the time) to be within the nonhazardous range.

Dr. Nordstrom's question about choice of control group lies at the center of what makes case-control studies difficult. We considered many options. We recruited and interviewed 2103 patients presenting to the emergency departments with medical problems other than injury. We have included them in the analyses for only one paper (J Stud Alcohol 2003; 64:733-740), however, because we found their pattern of alcohol use differed greatly from our population-based control group. Hospital controls for this study just weren't like the population from which the cases came, and that's what an appropriate control group must be.

Furthermore, as noted in the paper, we compared the pattern of drinking among our telephone controls with data from Missouri in the Behavioral Risk Factor Surveillance System. On the questions in the BRFSS, our controls were a close match to BRFSS data. We note, however, that both our community controls and BRFSS participants were recruited in the same way, random digit dialing. They may be similar because the samples have similar biases.

That's the beauty of comparing injured people with themselves the day before. The case and the control come from the same population; indeed, they are the same persons, perfectly matched. That leaves open other sources of bias, including notably recall bias (it's harder to recall how much you drank yesterday than today). But at least on the question of control group selection, there is no better group (if the research question at hand allows a case-crossover design).

We appreciate Dr. Heller's and Dr. Nordstrom's thoughtful comments and questions, and we look forward to hearing from other readers of the Annals.

Dan Vinson, MD

Competing interests:   None declared