Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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.
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 1
,Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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. 2
,Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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.
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 3
, Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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. 4
2021/2022.
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.
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 1
,Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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. 2
,Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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.
Webb, Bain & Page. Essential Epidemiology, 3rd Edn. 3
, Multiple_Choice_Questions_01_Questions_and_answers. Latest
2021/2022.
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. 4
