Affiliations of authors: P. B. Bach, D. Schrag, The Health Outcomes Research Group, Departments of Epidemiology and Biostatistics and of Medicine, Memorial Sloan-Kettering Cancer Center, New York, NY.
Correspondence to: Peter B. Bach, M.D., M.A.P.P., Health Outcomes Research Group, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., Box 221, New York, NY 10021 (e-mail: bachp{at}mskcc.org).
In a recent issue of the Journal, Woloshin et al. (1) presented age- and sex-specific 10-year risk charts for various causes of death for current smokers and nonsmokers. We believe that the estimates in the charts could be improved by 1) considering current smokers, former smokers, and never smokers as distinct groups when estimating individual risks from population rates; and 2) considering competing risks by accounting for the fact that a change in the absolute risk of a particular cause of death alters the risk of other causes of death.
One problem with Woloshin et al.s risk charts is that their estimated risks of lung cancer death among nonsmokers are higher than previously published estimates. For example, for a 70-year-old man who has never smoked, Woloshin et al. report a 10-year risk of lung cancer death of 1.2%. Estimates adapted from the Cancer Prevention Study II (2) and from the second wave of the British Physicians Study (3) are both about 0.4%. What accounts for the difference?
In the latter two studies, death rates were determined prospectively. Woloshin et al., by contrast, estimated risk in reverse, factoring the death rate in the entire population into the rates contributed by each of the risk groups. For example, lung cancer deaths among men in the population were separated into those occurring in current smokers and those occurring in never smokers. The rates of death within each of these groups were determined algebraically, based on both the published relative risks of death for current smokers relative to never smokers and the proportional representation of the two groups in the population. The proportional representation of current smokers was derived from survey data, whereas it appears that the proportional representation of never smokers was set to equal 1 minus this value, which in effect lumped never smokers and former smokers in the never smoker group.
Yet, for estimates of death rates to be accurate, all risk groups that both represent a sizable portion of the population and face a unique level of risk should be considered separatelythat is, heterogeneity must be limited. Because former smokers have roughly eight times the risk of lung cancer as never smokers, combining former and never smokers inflates the apparent risk among never smokers, which may cause needless alarm among this very low-risk segment of the population (4).
This omission would be minor if former smokers represented a small fraction of the population. However, in 2000 the majority of men older than 70 years were former, rather than current or never, smokers (Fig. 1). Had Woloshin et al. divided lung cancer deaths into three rather than two categories, the estimated risk of lung cancer among never smokers would have been reduced by about 60% (to about the same level reported in prospective studies). Furthermore, because the relationship between rates of lung cancer death in never smokers and current smokers is fixed by the relative risk, dividing lung cancer deaths into three risk groups reduces the estimated risk of lung cancer death for current smokers to the same extent.
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References
1 Woloshin S, Schwartz LM, Welch HG. Risk charts: putting cancer in context. J Natl Cancer Inst 2002;94:799804.
2 Thun M, Calle E, Rodriguez C, Wingo P. Epidemiological research at the American Cancer Society. Cancer Epidemiol Biomarkers Prev 2000;9:8618.
3 Doll R, Peto R, Wheatley K, Gray R, Sutherland I. Mortality in relation to smoking: 40 years observations on male British doctors. BMJ 1994;309:90111.
4 Thun MJ, Apicella LF, Henley SJ. Smoking vs other risk factors as the cause of smoking-attributable deaths: confounding in the courtroom. JAMA 2000;284:70612.
5 National Center for Health Statistics. National Health Interview Survey, 2000. Public-use data file and documentation 2002. [Last accessed 4/19/02.] Available at: ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Datasets/NHIS/2000.
6 Welch HG, Albertsen PC, Nease RF, Bubolz TA, Wasson JH. Estimating treatment benefits for the elderly: the effect of competing risks. Ann Intern Med 1996;124:57784.
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