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## Chapter 4

Measuring Disease Occurrence and Causal Effects

1. Suppose that in a population of 100 people, 30 die. The risk of death can be calculated as 30/100. What is missing from this measure?

2. Can we calculate a rate for the data in question 1? If so, what is it? If not, why not?

3. Eventually, all people die. Why should we not state that the mortality rate for any population is always 100%?

4. If incidence rates remain constant with time and if exposure causes disease, which will be greater, the risk ratio or the rate ratio?

5. Why is it incorrect to describe a rate ratio of 10 as indicating a high risk of disease among the exposed?

6. A newspaper article states that a disease has increased by 1200% in the past decade. What is the rate ratio that corresponds to this level of increase?

7. Another disease has increased by 20%. What is the rate ratio that corresponds to this increase?

8. From the data in Table 4–6, calculate the fraction of diarrhea cases among infants exposed to a low antibody level that is attributable to the low antibody level. Calculate the fraction of all diarrhea cases attributable to exposure to low antibody levels. What assumptions are needed to interpret the result as an attributable fraction?

9. What proportion of the 56 breast cancer cases in Table 4–7 is attributable to radiation exposure? What are the assumptions?

10. Suppose you worked for a health agency and had collected data on the incidence of lower back pain among people in different occupations. What measures of effect would you choose to look at, and why?

11. Suppose that the rate ratio measuring the relation between an exposure and a disease is 3 in two different countries. Would this situation imply that exposed people have the same risk in the two countries? Would it imply that the effect of the exposure is the same magnitude in the two countries? Why or why not?