A important study in the history of case-control methods was completed in 1950 by Doll & Hill. This study found that 647 of the 775 lung cancer cases were smokers. In contrast, 1,244 of 1,744 controls smoked. Calculate the measurement of association
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The odds ratio compares the odds of exposure (in this case, smoking) among the cases (lung cancer patients) to the odds of exposure among the controls. ** Show more…
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A causal relationship between cigarette smoking and lung cancer was first suspected in the 1920s on the basis of clinical observations. To test this apparent association, numerous epidemiologic studies were undertaken between 1930 and 1960. Two studies were conducted by Richard Doll and Austin Bradford Hill in Great Britain. The first was a case-control study begun in 1947 comparing the smoking habits of lung cancer patients with the smoking habits of other patients. The second was a cohort study begun in 1951 recording causes of death among British physicians in relation to smoking habits. This case study deals first with the case-control study, then with the cohort study. Data for the case-control study were obtained from hospitalized patients in London and vicinity over a four-year period (April 1948 – February 1952). Initially, 20 hospitals, and later more, were asked to notify the investigators of all patients admitted with a new diagnosis of lung cancer. These patients were then interviewed concerning smoking habits, as were controls selected from patients with other disorders (primarily nonmalignant) who were hospitalized in the same hospitals at the same time. Data for the cohort study were obtained from the population of all physicians listed in the British Medical Register who resided in England and Wales as of October 1951. Information about present and past smoking habits was obtained by questionnaire. Information about lung cancer came from death certificates and other mortality data recorded during ensuing years. Over 1700 patients with lung cancer, all under age 75 were eligible for the case-control study. About 15% of these persons were not interviewed because of death, discharge, severity of illness, or inability to speak English. An additional group of patients were interviewed by later excluded when initial lung cancer diagnosed proved mistaken. The final study group included 1,465 cases (1,357 males and 108 females). The following table shows the relationship between cigarette smoking and lung cancer among male cases and controls: Table 1 Cases Controls Cigarette Smoker 1,350 1,296 Nonsmoker 7 61 Total 1,357 1,357 Accurately calculate the odds ratio, with the correct equation. What do you infer from the odds ratio about the relationship between smoking and lung cancer?
Croup C.
EPIDEMIOLOGY A causal relationship between cigarette smoking and lung cancer was first suspected in the 1920s on the basis of clinical observations. Two studies were conducted by Richard Doll and Austin Bradford Hill in Great Britain. The first was a case-control study begun in 1947 comparing the smoking habits of lung cancer patients with the smoking habits of other patients. The second was a cohort study begun in 1951 recording causes of death among British physicians in relation to smoking habits. This case study deals first with the case-control study, then with the cohort study. Over 1,700 patients with lung cancer, all under age 75, were eligible for the case-control study. About 15% of these persons were not interviewed because of death, discharge, severity of illness, or inability to speak English. An additional group of patients were interviewed but later excluded when initial lung cancer diagnosis proved mistaken. The final study group included 1,465 cases (1,357 males and 108 females). The following table shows the relationship between cigarette smoking and lung cancer among male cases and controls. Table 1. Smoking status before onset of the present illness, lung cancer cases and matched controls with other diseases, Great Britain, 1948-1952. Exposure cases controls Smoker 1350 1296 Non-smoker 7 61 total 1357 1357 Question 1: Calculate the ratio of these odds. Question 2: What do you infer from the odds ratio about the relationship between smoking and lung cancer? Table 2 shows the frequency distribution of male cases and controls by average number of cigarettes smoked per day. Cigarettes/day Cases controls Odds ratio 0 7 61 Referent 1-14 565 706 15-24 445 408 25+ 340 182 All smokers 1350 1296 total 1357 1357 Question 3: Compute the odds ratio by category of daily cigarette consumption, comparing each smoking category to nonsmokers. Question 4: Interpret these results.
Sri K.
In one of the first studies of the link between lung cancer and smoking7, Richard Doll and Austin Bradford Hill collected data from 20 hospitals in London, England. Each patient admitted with lung cancer in the preceding year was queried about their smoking behavior. For each of the 709 patients admitted, they recorded the smoking behavior of a noncancer patient at the same hospital of the same gender and within the same 5-year grouping on age. A smoker was defined as a person who had smoked at least one cigarette a day for at least a year. Of the 709 cases having lung cancer, 688 reported being smokers. Of the 709 controls, 650 reported being smokers. - Estimate the odds ratio φ. - Construct a 95% confidence interval for log φ. - Suppose a 95% confidence interval for log φ is (a, b). Show that (exp(a), exp(b)) is a 95% confidence interval for φ.
Dr. C D.
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