Affiliations of authors: L. M. Schwartz, S. Woloshin, The VA Outcomes Group, Department of Veterans Affairs Medical Center, White River Junction, VT, The Center for the Evaluative Clinical Sciences, Dartmouth Medical School, Hanover, NH, and The Norris Cotton Cancer Center, Lebanon, NH; H. G. Welch, The VA Outcomes Group, White River Junction.
Correspondence to: Steven Woloshin, M.D., M.S., The VA Outcomes Group (111B), Department of Veterans Affairs Medical Center, White River Junction, VT 05009 (steven.woloshin{at}dartmouth.edu).
Bach and Schrag are correct that some of the simplifying assumptions used to create our risk charts introduce imprecision. We tried to make our methods transparent (i.e., avoid the problem of the black box) so others could understand, replicate, and perhaps improve on our work. To determine whether there is a genuine opportunity for improvement, however, it is probably best to review some of the choices we had to make.
Our idea was to create simple charts that could be posted anywhere (on the clinic office wall, for example) and did not require computer hardware. To make the charts easy to use, and to avoid data overload, we wanted to limit them to a single page. Consequently, we had to make pragmatic choices about which causes of death to include, the time frame for the risks, and the age groupings. Because causes of death differ for men and women in important ways, we decided to create separate charts for men and women.
After looking at the initial chartsand, in particular, at deaths from lung cancerwe realized we needed to account for smoking, which is arguably the most important risk factor for many of the causes of death (and all-cause mortality) shown in the charts. The best available estimates we found for the relative risk of death associated with smoking were derived from the American Cancer Societys Cancer Prevention Study (CPS-II)the source used in the Surgeon Generals report on the health effects of smoking (1). Nevertheless, we were concerned about the validity of the CPS-II estimates for former smokers because these estimates do not account for why the former smokers stopped smoking. Smokers who quit because they are sick (e.g., have developed lung cancer or have had a heart attack) will have worse health outcomes than "healthy" current smokers; paradoxically, giving up cigarettes will look dangerous. In the latest Surgeon Generals report about women and smoking (2), some efforts have been made to address the former-smoker problem (e.g., excluding former smokers who have quit within the last 2 years and those dying from cancer or heart disease within the first 2 years of the study); however, revised relative risk estimates are not yet available.
To avoid the former-smoker problem and to keep the number of charts manageable, we decided to create charts only for current and never smokers. The problem then was where to put the former smokers; we chose to group them with never smokers. Although this decision adds some imprecision to our estimates, the bias introduced is conservative. That is, we have been careful not to overstate the harm of smoking.
Bach and Schrag also note that we did not account for the fact that whatever increases the chance of dying from one cause must lower the chance of dying from other causes (because you can only die once). Addressing this issue would, however, require a complex model to account for relative changes in risk across diseases and over time. Although such a model might improve the precision of our estimates, it would require another layer of assumptions, potentially threatening the validity of the estimates. In addition, we wanted to keep our methods simple so that the charts could be readily updated to reflect the latest population statistics or expanded to include other conditions.
Finally, validating the charts is difficult because no clear external standards are available. Bach and Schrag use the observed 10-year risk of death among participants in the CPS-II and the British Physicians Study to suggest that our estimates (at least for lung cancer) may be slightly high: for a 70-year-old male never smoker, we reported a 12 in 1000 risk, compared with four in 1000 using those external standards. The problem here, however, is generalizability. Participants in both studies were, on average, healthier, of higher socioeconomic status, and more often white than the average American. It is not surprising that the risk of death observed in these selected populations would be a little lower than that of the general U.S. population. In fact, the Surgeon Generals reports recognize this lack of generalizabilitytheir calculations of lives lost from smoking use only the relative risks generated from CPS-II and then apply these to the population risks from the multiple cause of death file (3), just as our calculations did.
NOTES
Supported in part by Public Health Service grant CA 91052-01 from the National Cancer Institute, National Institutes of Health, Department of Health and Human Services. Drs. Woloshin and Schwartz are supported by Veterans Affairs Career Development Awards in Health Services Research and Development.
References
1 1989 Surgeon Generals report: reducing the health consequences of smoking. Chapter 3. Changes in smoking-attributable mortality. [Last accessed: 10/25/2001.] Available from: http://www.cdc.gov/tobacco/sgr/sgr_1989/1989SGRChapter3.pdf.
2 Women and smoking: a report of the surgeon general2001. Chapter 3. Health consequences of tobacco use among women. [Last accessed 8/28/2002.] Available from: http://www.cdc.gov/tobacco/sgr/sgr_forwomen/pdfs/chp3.pdf.
3 U.S. Department of Health and Human Services. 1998. Multiple cause-of-death file. National Center for Health Statistics CD-ROM Series 20 No. 10H. Issued December 2000.
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