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 experiments that might produce cancers or other serious damage, or to expose them to possibly noxious agents over the prolonged periods under strictly controlled conditions that would be necessary for a valid test. Therefore, the main evidence of the effects of smoking and other uses of tobacco upon the health of human beings has been secured through clinical and pathological observations of conditions occurring in men, women and children in the course of their lives, and by the application of epidemiological and statistical methods by which a vast array of information has been assembled and analyzed.

Among the epidemiological methods which have been used in attempts to determine whether smoking and other uses of tobacco affect the health of man, two types have been particularly useful and have furnished information of the greatest value for the work of this Committee. These are (1) retrospective studies which deal with data from the personal histories and medical and mortality records of human individuals in groups: and (2) prospective studies, in which men and women are chosen randomly or from some special group, such as a profession, and are followed from the time of their entry into the study for an indefinite period, or until they die or are lost on account of other events

Since 1939 there have been 29 retrospective studies of lung cancer alone which have varying degrees of completeness and validity. Following the publication of several notable retrospective studies in the years 1952–1956, the medical evidence tending to link cigarette smoking to cancer of the lung received particularly widespread attention. At this time, also, the critical counterattack upon retrospective studies and upon conclusions drawn from them was launched by unconvinced individuals and groups. The same types of criticism and skepticism have been, and are, marshalled against the methods, findings, and conclusions of the later prospective studies. They will he discussed further in Chapter 3, Criteria for Judgment, and in other chapters, especially Chapter 8. Mortality, and Chapter 9, Cancer.

During the decade 1950–1960, at various dates, statements based upon the accumulated evidence were issued by a number of organizations. These included the British Medical Research Council; the cancer societies of Denmark, Norway, Sweden, Finland, and the Netherlands; the American Cancer Society; the American Heart Association; the Joint Tuberculosis Council of Great Britain; and the Canadian National Department of Health and Welfare. The consensus, publicly declared, was that smoking is an important health hazard, particularly with respect to lung cancer and cardiovascular disease.

Early in 1954, the Tobacco Industry Research Committee (T.I.R.C.) was established by representatives of tobacco manufacturers, growers, and warehousemen to sponsor a program of research into questions of tobacco use and health. Since then, under a Scientific Director and a Scientific Advisory Board composed of nine scientists who maintain their respective institutional affiliations, the Tobacco Industry Research Committee has conducted a grants-in-aid program, collected information, and issued reports.

The U.S. Public Health Service first became officially engaged in an appraisal of the available data on smoking and health in June, 1956, under the instigation of the Surgeon General, a scientific Study Group on 6