Question 1

What is the difference between the incidence proportion and the incidence rate?

Accepted Answer

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.

Question 2

According to the table below, which food is the most likely cause of the outbreak of food poisoning?

Accepted Answer

The potato salad is the most likely culprit because it has the highest attack
rate (38 ÷ 54 = 70.4%).This can't be definitive, given the challenges of recall and the fact
that most people will eat a number of foods in addition to that causing the problem, but
it (and to a lesser extent the egg sandwiches, attack rate = 40 ÷ 76 = 52.6%) stand out
from the crowd, and both are known to be potential sources of food poisoning. 11ebbba8_3415_1a5b_bcf2_018ffabb8a5a_TB8436_00 11ebbba8_3415_1a5c_bcf2_cd2f20a7f268_TB8436_00

Question 3

Inastudyof500patientswithcoronaryheartdisease,100alreadyhaddiabeteswhenthestudystartedon1January2014.Overthenextyear,50moredevelopeddiabetes.(Assumethediabetesispermanentandtherearenolossesorentriestothegroupofpatientswithheartdisease.)
-What is the prevalence of diabetes at the start of 2014?

Accepted Answer

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%.

Question 4

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:

Accepted Answer

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).

Question 5

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?

Accepted Answer

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
denominator without a change in the numerator (C) necessarily reduces the size of the
measure.

Question 6

Inastudyof500patientswithcoronaryheartdisease,100alreadyhaddiabeteswhenthestudystartedon1January2014.Overthenextyear,50moredevelopeddiabetes.(Assumethediabetesispermanentandtherearenolossesorentriestothegroupofpatientswithheartdisease.)
-What is the incidence proportion of diabetes in the same study?

Accepted Answer

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.

Question 7

The following table shows data from an epidemiological study.What is the incidence rate among those who are exposed to the factor under study?

Accepted Answer

The incidence rate in the exposed = 700 ÷ 1950 py = 0.359 = 35.9 per 100 py.
It would be 359 per 1000 py (C) or 35,900 per 100,000 py (B).

Question 8

A new treatment is developed that prevents death but does not produce recovery from a previously lethal disease.Which of the following will occur?

Accepted Answer

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.

Question 9

The following are all characteristics of the prevalence of a disease except one, which one?

Accepted Answer

Prevalence is measured at a single point in time.(An exception is period
prevalence which counts all cases that were present at some point during a given time
window).

Question 10

A 50 year old Australian male is watching the news in 2014 and hears that the current life expectancy for males has risen to 80 years.Does this mean he can expect to live
For another 30 years?

Accepted Answer

No.If life‐expectancy at birth is 80 years and he has already lived for 50
years, he can expect to live longer than 80 years, because the probability of dying differs
over the life‐course.This expectation can be calculated from the life table, and if he has
reached 50 an Australian man can expect to live another 32 years and reach 82.The
difference used to be much greater when there were many more deaths in early life.
(And remember, this expectation is calculated on current death rates, so the true
expectation is probably longer again, given continuing improvements in health care and
prevention.)

Question 11

Community A and community B both have crude mortality rates for ischaemic heart disease (IHD) of 4 per 1000 population per year but the age‐adjusted IHD mortality
Rate in community A is 5 per 1000 population compared to 3 per 1000 population in
Community B.Which of the following is correct?

Accepted Answer

Mortality from IHD increases with age.If the age‐adjusted rate is higher than
the crude rate in population A then, on average, population A must be younger than the
standard population.In contrast, the age‐adjusted rate in population B is lower than the
crude rate so this population must, on average, be older than the standard population.
Community A therefore has a younger population than community B.The accuracy of
diagnosis (C, D) is irrelevant.

Quiz 2: How Long Is a Piece of String Measuring Disease Frequency

What is the difference between the incidence proportion and the incidence rate?

According to the table below, which food is the most likely cause of the outbreak of food poisoning?

Inastudyof500patientswithcoronaryheartdisease,100alreadyhaddiabeteswhenthestudystartedon1January2014.Overthenextyear,50moredevelopeddiabetes.(Assumethediabetesispermanentandtherearenolossesorentriestothegroupofpatientswithheartdisease.) -What is the prevalence of diabetes at the start of 2014?

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 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?

The following table shows data from an epidemiological study.What is the incidence rate among those who are exposed to the factor under study?

A new treatment is developed that prevents death but does not produce recovery from a previously lethal disease.Which of the following will occur?

The following are all characteristics of the prevalence of a disease except one, which one?

A 50 year old Australian male is watching the news in 2014 and hears that the current life expectancy for males has risen to 80 years.Does this mean he can expect to live For another 30 years?

Community A and community B both have crude mortality rates for ischaemic heart disease (IHD) of 4 per 1000 population per year but the age‐adjusted IHD mortality Rate in community A is 5 per 1000 population compared to 3 per 1000 population in Community B.Which of the following is correct?