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:

1. Accurately calculate the proportion of cases that smoked. Be sure to show your calculations.

2. Accurately calculate the proportion of controls that smoked. Be sure to show your calculations.

3. 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? 

Table 2 shows the frequency distribution of male cases and controls by average number of cigarettes smoked per day.

Table 2: Daily cigarette consumption

4. Accurately calculate the odds ratios by category of daily cigarette consumption, comparing each category to nonsmokers. Be sure to show your calculations.

5. Interpret these results, and describe the trends or patterns you see in the data.