Essential Epidemiology
Multiple Choice 1
CHAPTER 2
In a study of 500 patients with coronary heart disease, 100 already had diabetes when
the study started on 1 January 2014. Over the next year, 50 more developed diabetes.
(Assume the diabetes is permanent and there are no losses or entries to the group of
patients with heart disease.)
1. What is the prevalence of diabetes at the start of 2014?
A. 30%
B. 2%
C. 20%
D. 12.5%
Answer: C. 100 of 500 people had diabetes at the start of 2014 and 100 ÷ 500 = 0.2 or
20%. The prevalence of diabetes at the end of 2014 would be 30% (A) as it includes the
new cases diagnosed during the study: (100 + 50) ÷ 500 = 150 ÷ 500 = 0.3 or 30%.
2. What is the incidence proportion of diabetes in the same study?
A. 30%
B. 12.5%
C. 20%
D. 12.5% over 1 year
Answer: D. 50 ÷ (500 – 100) = 0.125 or 12.5% over 1 year. Note that we must exclude
the 100 people who already have diabetes from the denominator and the period over
which the cases accumulate must be given.
3. At the beginning of 1999, 2.3% of the Australian population were estimated to be
infected with Hepatitis C virus (HCV). During the year 1999, a further 16,000
individuals were found to have HCV. From this information we can conclude:
A. The incidence rate is 2.3%
B. The point prevalence is 2.3%
C. The incidence proportion is 2.3%
D. None of the above
Answer: B. The point prevalence is 2.3% at the beginning of 1999. We are told that 2.3%
of the population were infected at the start of the year – as they are already infected
this is a measure of prevalence. As we do not know the total population at risk of HCV
infection we cannot calculate either an incidence rate (A) or incidence proportion (C).
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 1
, Essential Epidemiology
4. What is the difference between the incidence proportion and the incidence rate?
A. The incidence proportion measures the proportion of people who develop disease
during a specified period, whereas the incidence rate measures how quickly people
are developing disease
B. The incidence proportion measures how quickly people are developing disease,
whereas the incidence rate measures the proportion of people who develop disease
during a specified period
C. The incidence proportion measures the number of people with disease in a
population at a specific point in time, whereas the incidence rate measures the
number of new cases of disease that occur in the population.
D. None of the above
Answer: A. The incidence proportion measures the proportion of people who develop
disease during a specified period. It presents the number of new cases in a designated
time period (the numerator) as a proportion of the total number of people at risk at the
start of the period (the denominator) and has no units e.g. 1% (in six months). In
contrast, the incidence rate measures how quickly people are developing disease over
time and it has units of time e.g. 10 per 1000 per year.
5. A new treatment is developed that prevents death but does not produce recovery
from a previously lethal disease. Which of the following will occur?
A. Prevalence will increase
B. Prevalence will decrease
C. Incidence will increase
D. Incidence will decrease
Answer: A. Prevalence is a function of incidence (the rate at which new cases of disease
occur) and duration (how long an incident case continues to have the disease). If cases
no longer die from the disease their duration of life with the disease present necessarily
increases, hence prevalence increases. The new treatment will not, however, affect how
quickly new cases occur so it will not affect the incidence of the disease.
6. A study aims to determine the incidence and prevalence of a particular disease within
the local government area of Winchelsea. What factors would decrease the
prevalence of the disease within this study catchment area?
A. Shorter duration of disease
B. Increasing case‐fatality from the disease
C. In‐migration of healthy people to the area
D. All of the above
Answer: D. All of the above. Prevalence is a function of incidence (the rate at which new
cases of disease occur) and duration (how long an incident case continues to have the
disease). A and B both reduce the time people have the disease, while an increase in the
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 2
Multiple Choice 1
CHAPTER 2
In a study of 500 patients with coronary heart disease, 100 already had diabetes when
the study started on 1 January 2014. Over the next year, 50 more developed diabetes.
(Assume the diabetes is permanent and there are no losses or entries to the group of
patients with heart disease.)
1. What is the prevalence of diabetes at the start of 2014?
A. 30%
B. 2%
C. 20%
D. 12.5%
Answer: C. 100 of 500 people had diabetes at the start of 2014 and 100 ÷ 500 = 0.2 or
20%. The prevalence of diabetes at the end of 2014 would be 30% (A) as it includes the
new cases diagnosed during the study: (100 + 50) ÷ 500 = 150 ÷ 500 = 0.3 or 30%.
2. What is the incidence proportion of diabetes in the same study?
A. 30%
B. 12.5%
C. 20%
D. 12.5% over 1 year
Answer: D. 50 ÷ (500 – 100) = 0.125 or 12.5% over 1 year. Note that we must exclude
the 100 people who already have diabetes from the denominator and the period over
which the cases accumulate must be given.
3. At the beginning of 1999, 2.3% of the Australian population were estimated to be
infected with Hepatitis C virus (HCV). During the year 1999, a further 16,000
individuals were found to have HCV. From this information we can conclude:
A. The incidence rate is 2.3%
B. The point prevalence is 2.3%
C. The incidence proportion is 2.3%
D. None of the above
Answer: B. The point prevalence is 2.3% at the beginning of 1999. We are told that 2.3%
of the population were infected at the start of the year – as they are already infected
this is a measure of prevalence. As we do not know the total population at risk of HCV
infection we cannot calculate either an incidence rate (A) or incidence proportion (C).
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 1
, Essential Epidemiology
4. What is the difference between the incidence proportion and the incidence rate?
A. The incidence proportion measures the proportion of people who develop disease
during a specified period, whereas the incidence rate measures how quickly people
are developing disease
B. The incidence proportion measures how quickly people are developing disease,
whereas the incidence rate measures the proportion of people who develop disease
during a specified period
C. The incidence proportion measures the number of people with disease in a
population at a specific point in time, whereas the incidence rate measures the
number of new cases of disease that occur in the population.
D. None of the above
Answer: A. The incidence proportion measures the proportion of people who develop
disease during a specified period. It presents the number of new cases in a designated
time period (the numerator) as a proportion of the total number of people at risk at the
start of the period (the denominator) and has no units e.g. 1% (in six months). In
contrast, the incidence rate measures how quickly people are developing disease over
time and it has units of time e.g. 10 per 1000 per year.
5. A new treatment is developed that prevents death but does not produce recovery
from a previously lethal disease. Which of the following will occur?
A. Prevalence will increase
B. Prevalence will decrease
C. Incidence will increase
D. Incidence will decrease
Answer: A. Prevalence is a function of incidence (the rate at which new cases of disease
occur) and duration (how long an incident case continues to have the disease). If cases
no longer die from the disease their duration of life with the disease present necessarily
increases, hence prevalence increases. The new treatment will not, however, affect how
quickly new cases occur so it will not affect the incidence of the disease.
6. A study aims to determine the incidence and prevalence of a particular disease within
the local government area of Winchelsea. What factors would decrease the
prevalence of the disease within this study catchment area?
A. Shorter duration of disease
B. Increasing case‐fatality from the disease
C. In‐migration of healthy people to the area
D. All of the above
Answer: D. All of the above. Prevalence is a function of incidence (the rate at which new
cases of disease occur) and duration (how long an incident case continues to have the
disease). A and B both reduce the time people have the disease, while an increase in the
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 2
