QuestionTEST YOURSELF: Consider a source population consisting of 1,000 adults. Assume that no subjects moved in or out of the population over the next 12 years, but there were some deaths. Among the 1,000 subjects, 990 remained alive and free of cancer from 2001 to 2012. Events in the other 10 subjects are depicted in the image below. Subjects $1,2,3$, and 4 were known to have lung cancer in 2001. Dashed lines indicate the ongoing presence of lung cancer in living subjects (dashed lines), and deaths are indicated in the figure.
For this exercise answer the questions below as simple fractions showing the numerator and the denominator in order to make sure you understand prevalence. (Ordinarily, you would compute the decimal fraction and express in as, e.g., 7 per 1,000 population in 2007). Compute your own answers before looking at the correct answer.
Question 1: What was the prevalence of lung cancer in 2001? Answer:
Question 2: What was the prevalence of lung cancer in 2007? Answer:
Question 3: What was the prevalence of lung cancer in 2012? Answer