Published on January 19, 2016
1. ANGAD SINGH MSC. BIOSTATISTICS AND DEMOGRAPHY 2015-17
2. CONTENT : - • About case control study. • History of cigarette smoking. • About Sir Dolls Richard. • Dolls case control study. • Results • Conclusion
3. Case control study definitions: A study that compares two groups of people: those with the disease or condition under study (cases) and a very similar group of people who do not have the disease or condition (controls). (National Institute of Health, USA) A case control study involves two populations – cases and controls and has three distinct features : Both exposure and outcome have occurred before the start of the study. The study proceeds backwards from effect to cause. It uses a control or comparison group to support or refute an inference. (Park’s Textbook of Preventive and Social Medicine – 20th ed; K. Park. 2009) Definitions:
4. Case : A person in the population or study group identified as having the particular disease, health disorder or condition under investigation. (Dictionary of Epidemiology: 3rd ed; John M Last. 2000) Control: Person or persons in a comparison group that differs, in disease experience (or other health related outcome) in not having the outcome being studied. (Dictionary of Epidemiology: 3rd ed; John M Last. 2000) Definitions:
5. History of Cigarette Smoking - 1912: In a monograph, Dr. Isaac Adler is the first to strongly suggest that lung cancer is related to smoking. - 1928: German scientist proposes that lung cancers among non-smoking women could be caused by inhalation of their husbands' smoke. - 1930: US has a per capita smoking rate of 977 cigarettes/year. - 1930: 2,357 cases of lung cancer reported in the US. The lung cancer death rate in white males is 3.8 per 100,000. - 1939-1945: WORLD WAR II. As part of the war effort, Roosevelt makes tobacco a protected crop. Cigarettes are included in GI's C-Rations. Tobacco companies send millions of free cigarettes to GI's, mostly the popular brands. - 1948: UK: Sir Richard Doll has written: On I January 1948, "The First Reports on Smoking and Lung Cancer". - 1948: Lung cancer has grown 5 times faster than other cancers since 1938; behind stomach cancer. - 1950: Three important epidemiological studies provide the first powerful links between smoking and lung cancer. All of them the retrospective case-control method. • In May 27, 1950 issue of JAMA, Morton Levin publishes first major study definitively linking smoking to lung cancer. • In the same issue, "Tobacco Smoking as a Possible Etiologic Factor in Bronchiogenic Carcinoma: A Study of 684 Proved Cases," by Ernst L. Wynder and Evarts A. Graham of the United States, found that 96.5% of lung cancer patients interviewed were moderate heavy-to-chain-smokers. • 1950-09:30: RICHARD DOLL and A BRADFORD HILL publish first report on Smoking and Carcinoma of the Lung in the British Medical Journal, finding that heavy smokers were fifty times as likely as nonsmokers to contract lung cancer. The cancer advisory Committee of the Ministry of Health says they have demonstrated an association, not a cause, and advise the Government to do nothing.
6. Smoking & Lung Cancer Tobacco is a dirty weed. I like it. It satisfies no normal need. I like it. It makes you thin, it makes you lean, It takes the hair right off your bean. It's the worst darn stuff I've ever seen. I like it. Graham Lee Hemminger, Penn State Froth, Tobacco (1915)
7. OBJECTIVE AND DESIGN: To relate UK national trends since 1950 in smoking, in smoking cessation, and in lung cancer to the contrasting results from two large case-control studies centred around 1950 and 1990. SETTING: United Kingdom. PARTICIPANTS: Hospital patients under 75 years of age with and without lung cancer in 1950 and 1990, plus, in 1990, a matched sample of the local population: 1465 case-control pairs in the 1950 study, and 982 cases plus 3185 controls in the 1990 study. MAIN OUTCOME MEASURES: Smoking prevalence and lung cancer.
8. Methods :- The 1950 study was conducted in London and four other large towns during 1948-52, and It involved interviewing, as potential “cases,” patients younger than 75 years of age in hospital for suspected lung cancer and, as “controls,” age matched patients in hospital with various other diseases (some of which would, in retrospect, have been conditions associated with smoking). After patients in whom the initial diagnosis of lung cancer was eventually refuted were excluded from the cases, 1465 cases and 1465 controls remained. A preliminary report on 709 case-control pairs was published in 1950, and the full results were published two years later.
9. Trends in prevalence of smoking at ages 35–59 (left) and ≥60 (right) in men and women in the United Kingdom, 1950-98. Prevalence at ages 25–34 were 80% for men and 53% for women in 1948–52 and 39% for men and 33% for women in 1998.
10. Trends in mortality from lung cancer in men and women in the United Kingdom, 1950-97: annual mortality per 105 at ages 35–54 (left) and 55–74 (right) years. Rate in each 20 year age range is mean of rates in the four component five year age groups.
11. Effects of stopping smoking at various ages on the cumulative risk (%) of death from lung cancer up to age 75, at death rates for men in United Kingdom in 1990. (Non-smoker risks are taken from a US prospective study of mortality
12. RESULTS: For men in early middle age in the United Kingdom the prevalence of smoking halved between 1950 and 1990 but the death rate from lung cancer at ages 35–54 fell even more rapidly, indicating some reduction in the risk among continuing smokers. In contrast, women and older men who were still current smokers in 1990 were more likely than those in 1950 to have been persistent cigarette smokers throughout adult life and so had higher lung cancer rates than current smokers in 1950. The cumulative risk of death from lung cancer by age 75 (in the absence of other causes of death) rose from 6% at 1950 rates to 16% at 1990 rates in male cigarette smokers, and from 1% to 10% in female cigarette smokers. Among both men and women in 1990, however, the former smokers had only a fraction of the lung cancer rate of continuing smokers, and this fraction fell steeply with time since stopping. By 1990 cessation had almost halved the number of lung cancers that would have been expected if the former smokers had continued. For men who stopped at ages 60, 50, 40, and 30 the cumulative risks of lung cancer by age 75 were 10%, 6%, 3%, and 2%.
13. CONCLUSIONS: People who stop smoking, even well into middle age, avoid most of their subsequent risk of lung cancer, and stopping before middle age avoids more than 90% of the risk attributable to tobacco. Mortality in the near future and throughout the first half of the 21st century could be substantially reduced by current smokers giving up the habit. In contrast, the extent to which young people henceforth become persistent smokers will affect mortality rates chiefly in the middle or second half of the 21st century.
14. What is already known on this topic Smoking is a cause of most deaths from lung cancer in the United Kingdom Early studies could not reliably assess the effects of prolonged cigarette smoking or of prolonged cessation What this study adds If people who have been smoking for many years stop, even well into middle age, they avoid most of their subsequent risk of lung cancer Stopping smoking before middle age avoids more than 90% of the risk attributable to tobacco Widespread cessation of smoking in the United Kingdom has already approximately halved the lung cancer mortality that would have been expected if former smokers had continued to smoke As most current smokers in the United Kingdom have consumed substantial numbers of cigarettes throughout adult life, their risks of death from lung cancer are greater than earlier studies had suggested Mortality from tobacco in the first half of the 21st century will be affected much more by the number of adult smokers who stop than by the number of adolescents who start
15. Sources:- Doll R. Uncovering the effects of smoking: historical perspective. Stat Methods Doll R, Hill AB , Smoking and carcinoma of the lung. Preliminary report.1950 Doll R, Hill AB, A study of the aetiology of carcinoma of the lung http://www.bmj.com/
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Centers for Disease Control and Prevention Epidemiology Program Office Case Studies in Applied Epidemiology No. 731-703 Cigarette Smoking and Lung Cancer