Mortality and the Business Cycle: How Far Can We Push an Association? EDWARD A. LEW, FSA The marked decline in mortality from heart disease over the past 15 years appears likely to spur new etiologic hypotheses linking heart disease to one or more specific factors in an explicit way. Statistics on heart disease provide a point of departure, but the more than 60-years-long series of heart disease death rates is neither homogeneous nor comparable in time. Although mathematical models promote more rigorous thinking, their use can lull the unsuspecting into believing that he who reasons elaborately reasons well even about such complex phenomena as heart disease. One must be cautious, however, because some mathematical models strip away large parts of the problem, some may be inappropriate for the soft data available, and some may introduce unwarranted assumptions. Etiologic hypotheses in other fields need to be no less carefully scrutinized, especially when based on limited, biased or hard to interpret material or when employing mathematical models that subjoin implicit assumptions. Several of these issues can be illustrated by reference to the paper "Ischemic Heart Disease Mortality and the Business Cycle in Australia" I by an Australian economist, R. A. Dunn, published in this issue of the Journal. The author builds on an established association between heart disease and unemployment, as well as an index of national stress, in order to postulate that the trend of heart disease in Australia can be represented by parabolic curves. From these curves he forecasts a discontinuity in the downward trend of IHD death rates in Australia during 1976-1978. As I see it, the paper has several serious flaws which stem from the author's unqualified acceptance of IHD death rates as a homogeneous and meaningful time series, from his belief that the increase in mortality from heart disease since the great depression constituted an epidemic of heart disease, and from his faith Address reprint requests to Edward A. Lew, FSA, Project Director and Co-editor, Mortality Monograph Committee, Association of Life Insurance Medical Directors of America and Society of Actuaries, Route 1, Box 745, Punta Gorda, FL 33950. A retired vicepresident and actuary with the Metropolitan Life Insurance Company, he is a past president of the Society of Actuaries, a fellow of the Council on Epidemiology, American Heart Association, and an honorary member of the Association of Life Insurance Medical Directors of America. He is the author of numerous articles on medical statistics. Editor's Note: See also editorial, page 762, this issue, as well as accompanying articles, pages 772, 784, and 789.

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in curve fitting as a predictive model. The forecast based on this model has not been borne out by statistics in the United States. The author calculated a series of IHD death rates for Australia, beginning in 1930, by bridging successive revisions of the International Classification of Diseases and by interpolating for earlier periods. He did not stop to consider whether the rates so developed provided figures valid for curve fitting. Heart disease death rates compiled in the United States and Western Europe for the years since 1930 have been markedly affected by radical changes in the concept of heart disease and by related modifications in the reporting and coding of this disease as a cause of death. At the turn of the century, the international list of causes of death devoted only four rubrics to heart disease. Two decades later, Herrick's classic delineation of coronary heart disease had not yet gained general acceptance as a separate clinical entity, and it was not until 1929 that a code for coronary heart disease and angina pectoris was officially adopted. The category of heart disease was enlarged during the ensuing decade by a diagnostic shift from chronic valvular disease and from some forms of acute heart disease to myocardial infarction and coronary artery disease. The ingathering of physicians in the armed forces during World War II pushed the diagnosis of coronary artery disease to the fore. Medical examiners came to use this label more and more in cases of sudden death and cases where the deceased had not received medical treatment. The diagnosis of coronary artery disease was accepted first in those areas of the United States which had advanced medical standards, while areas with poor medical facilities continued to use the more traditional designations. This produced a continued uptrend in coronary artery disease for the country as a whole even after death rates from this condition had stabilized in areas where it had been recognized early. The same kind of lag was observed later with respect to the more comprehensive diagnosis of arteriosclerotic heart disease and with respect ot the IHD designation. The expanding concepts of heart disease and the associated new rules for coding this disease as a cause of death resulted in a steadily mounting number of deaths attributed to heart disease and hence in an increase in death rates from heart disease. Those seeking to dramatize the situation called the increase an epidemic. This was a misnomer, in that mortality AJPH August 1979, Vol. 69, No. 8

PUSHING CAUSAL RELATIONSHIPS AND MORTALITY

from heart disease recorded a gradual increase over a long period of time and reflected in substantial measure a transfer of deaths from other cardiovascular renal diseases, whereas the term epidemic had been used in a specific sense for infectious diseases to characterize a sudden sharp outbreak to unaccustomed levels. Nevertheless, the author saw the increase in heart disease mortality since 1930 as an epidemic. He gave no reasons for this position except to say "'the mortality trend describes a typical epidemic parabolic path from the great depression to 1975, with a smaller parabolic trend at the 1961 recession."' After making the unwarranted asumption of an epidemic of heart disease, he proceeded to fit parabolic curves to the series of IHD death rates he had developed, with the comment that presumably was intended to justify his curve fitting, as follows: "The near perfect values of the coefficients indicate that the path of the epidemic for these age groups is parabolic for 1930-1975." 1 Should the anticipated discontinuity in the downtrend of IHD death rates in Australia fail to materialize during 1976-1978, we will have yet another demonstration that a curve can always be fitted to a preconceived notion. In singling out the stress factor as the principal element dominating the trend of heart disease mortality, without any explanation for doing so, the author had downgraded the many factors whose effects have been well established. He has notably underplayed the effects of more widespread and more successful antihypertensive treatment, the decrease in cigarette smoking and reduction in tar and nicotine content of cigarettes, improved medical care of heart cases (including earlier admission to hospital and coronary care units), absence of severe outbreaks of influenza and more reasonable diet patterns.

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There is clearly a possibility of professional bias in having economists interpret heart disease trends by reference to changes in the economy, or having sociologists interpret these trends largely by reference to changes in life-styles, or even environmentalists interpret heart disease trends in terms of changes in the ecology. In recent years, attempts have been made by various biased groups to dramatize changes in cancer death rates as portending an epidemic of this disease in industrialized countries. Such groups have given us their particular views on potential carcinogens and on the impact of such carcinogens on mortality. Some of the etiologic hypotheses proposed have been elevated to the status of prediction models, even when based on tenuous associations or highly dubious bioassays. Dire consequences have been projected from scanty observations or from animal experiments of questionable relevance. The tests used have probably exonerated as many harmful substances as they have thrust into the limelight reserved for new carcinogens. More definitive studies and better bioassays are obviously required to settle such important issues. We must insist on studies and experiments of unquestioned quality and depth, and shun publication of "'interesting findings" that carry little weight. There is a pressing need to reinstate stringent scientific standards and reestablish credibility with the public for the content of scientific journals.

REFERENCES 1. Bunn AR: Ischaemic heart disease mortality and the business cycle in Australia. Am J Public Health 69:772-781, 1979.

Research Grants Offered by Leukemia Society of America

The Leukemia Society of America, Inc., is now accepting applications for grants to support research in the fields of leukemia and related disorders. As an important source of funding for individual investigators whose work is concentrated on uncovering the cause or cure for leukemia, the lymphomas and Hodgkin's disease, the national voluntary agency offers three types of awards. The grants are intended to encourage studies at both the basic science and clinical levels. Five-year scholarships for a total of $100,000 are available for researchers who have demonstrated their ability to conduct original investigations in the specified fields. Two-year special fellowships and fellowships for $31,000 and $25,000, respectively, are offered for those in the intermediate and entry stages of career development. In all categories, candidates must hold a doctoral degree but may not have attained the tenured status of associate professor. There are no restrictions as to age, citizenship, race, religion or sex. Deadline for filing applications is September 1, 1979, a month earlier than previously due to the increase in the number of proposals received last year and the extra time involved in reviewing them. Only one application in the scholar and special fellow categories will be accepted from a prospective sponsoring organization, although duplicates are permitted for fellows. Project proposals will be evaluated on a competitive basis by the Society's volunteer Medical and Scientific Advisory Committee, 19 specialists who also serve on the agency's National Board of Trustees. The reviews will take place in January 1980 with funding to start July 1, 1980. Application forms and further information may be obtained by writing to Dr. Kenneth McCredie, Vice President for Medical and Scientific Affairs, Leukemia Society of America, Inc., 211 East 43 St., New York, NY 10017. AJPH August 1979, Vol. 69, No. 8

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Mortality and the business cycle: how far can we push an association?

Mortality and the Business Cycle: How Far Can We Push an Association? EDWARD A. LEW, FSA The marked decline in mortality from heart disease over the p...
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