Posted: October 3rd, 2016

What are the different types of biases that can occur in a screening program? Explain

23. 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 with the case-control study.

Data for the case-control study were obtained from hospitalized patients in London and vicinity over a 4-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 non-malignant) who were hospitalized in the same hospitals at the same time.

The 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, 1948-1952

Cases Controls
Cigarette smoker

Non smoker

1,465 1,465
a. How representative of all persons with lung cancer are hospitalized patients with lung
cancer? [ONE POINT]

b. How representative of the general population without lung cancer are hospitalized
patients without lung cancer? [ONE POINT]
c. Estimate the odds ratio from the data in table 1 and interpret the odds ratio. [ONE POINT]

24. During July 2014, a county health department received reports of 12 new cases of measles. What additional information is needed to determine whether this group of cases is an outbreak? [ONE POINT]

25. What are the different types of screening programs? Give example of each type. [TWO POINTS]
26. What are the different types of biases that can occur in a screening program? Explain. [ONE POINT]