REVIEW QUESTIONS for Chapter 6 

�6.1 Background

1. What is the difference between a prevalence count and incidence count? 
2. More people die each year in New York City each year than in any other U. S. city. Does this mean that New York City is a risky place to live? Explain.
3. Incidence counts should be considered in relation to the ___________ of the population from which the cases arose.
4. What is a ratio? 
5. Provide a synonym for closed population.
6. What is a stationary population?
7. Can stationary populations ever be closed? Explain.
8. What happens to the average age of a cohort over time?
9. What happens to the size of a cohort over time? Explain.
10. Can an open population increase in size over time? Explain. 
11. Ollie Miettinen once said �once you are a member of a cohort, you are a member for life.� Explain the meaning of this statement.

�6.2 Incidence Proportion (Risk, Cumulative Incidence)

1. What goes into the numerator of an incidence proportion? 
2. What goes into the denominator of an incidence proportion?
3. Why do denominators of incidence proportions exclude those who are not at risk?
4. List synonyms for incidence proportion.
5. A group of women demonstrates a 5% risk of breast cancer. What additional information is needed to interpret this statement? 
6. A group shows a one-year risk of 0.025. Express this risk in terms of a uni-cohort, that is, the size of a cohort that is expected to generate one case (Table 6.1, p. 128, note a).
7. Perception of risk often differs from reality. Identify factors that shape misapprehensions of risk.
8. Are children at greater risk of kidnapping by a stranger or being struck by lightening? (Table 6.1)
9. Suppose we calculate the number of deaths in a community in a year and divide this number by the number of people living in the community at a particular time. Is this a risk or a rate? Explain.

�6.3 Incidence Rate (Incidence Density)

1. Propose three different ways to generate a person-year.
2. A carpenter works 60 hours fixing your kitchen. A tile layer works 8 hours on your kitchen. How many person-hours accumulated on the job? 
3. What information goes into the numerator of an incidence rate? What goes into the denominator?
4. List two synonyms for incidence rate.
5. What are the units of an incidence rate? 
6. A stationary population demonstrates a mortality rate of 0.01333 year^-1.  What is the life expectancy in this population?
7. A different stationary population demonstrates a life expectancy of 80 years. What is the mortality rate in this population?
8. Express the rate 0.01333 year^-1 with a 1000 person-year multiplier.
9. An open population with an average population size of 295 people experiences 2 deaths in a given year. What is the mortality rate in this population?
10. An open population with an average population size of 295 people experiences 4 deaths over two years. What is the mortality rate in this population?
11. Under what condition is an incidence rate equal to an incidence proportion?

�6.4 Prevalence

1. What goes into the numerator of a prevalence calculation? 
2. What goes into the denominator of prevalence?
3. What units are associated with prevalence estimates?
4. List ways in which prevalence differs from incidence.
5. If the rate of a disease remains constant, but the death rate of the disease decreases (through improved treatment), what happens to its prevalence of the condition over time?
6. Match each term with its description.
   Terms: risk, rate, prevalence
   Descriptions: 
   (a) Estimated probability an individual selected at random from the population will have the condition in question
   (b) Estimated probability an individual selected at random from the population will develop the condition in question over a stated period of time.
   (c) �Speed� at which events occur in the population.

Answers (may not be posted) �������������� Last Update: 11/05/2008