11.1.1 Epidemiology

A Search For Better Health
Topic 11: Epidemiology
Biology in Focus, HSC Course
Glenda Childrawi, Margaret Robson and Stephanie Hollis
DOT Point(s)
 identify and describe the main features of
epidemiology using lung cancer as an example
The incidence of a particular disease, the cause of which is
unknown, is increasing in a population. This disease is causing
severe symptoms for the sufferers, and quite often results in death.
This leads scientists to ask the
questions: Is there a pattern to
the occurrence of this disease?
What could be the cause of this
disease? What control measures
can be put in place to help
prevent this disease? In order to
answer these questions about
the disease, an epidemiological
study could be undertaken.
Epidemiological studies play a major role in identifying patterns in
the occurrence of disease, identifying the possible cause of disease
and determining the strategies that would be most effective in
controlling disease in the population.
 Epidemiology is the scientific
study of patterns of
occurrence of disease in
human populations and the
factors that affect these
 It describes, statistically
analyses and hypothesises as to
the cause of the disease in the
 Epidemiology can be used to study both infectious and non-
infectious diseases as well as events such as suicides, car
accidents and work-related accidents.
 Results from epidemiological studies are used by public health
authorities to develop strategies to control disease and improve
public health. Epidemiological studies can also be used to
evaluate those strategies that are already in place.
There are three major types of epidemiological studies:
1. descriptive
2. analytical
3. intervention.
1. Descriptive studies are usually the
first type of study completed when
investigating the cause of a disease.
These provide information about the
patterns of the disease, including the
frequency of the disease, which section
of the population is affected (age,
gender, occupation, socioeconomic
status and so on), the geographical
location and whether there was a
particular time period in which
individuals were affected.
In an early epidemiological study launched to determine the cause
of lung cancer, the data collected included, amongst other things,
information about the age, sex, smoking habits, diet, occupation
and drinking habits of both smokers and non-smokers.
2. Analytical studies occur
once a descriptive study has been
completed and are used to collect
more data, which is then
statistically analysed to develop
hypotheses as to the likely
cause(s) of the disease. The
morbidity (number of cases of the
disease) and the mortality
(percentage of the population that
dies from the disease) are two
indicators that can be used in
these studies.
Data about the incidence (number of new cases in a specific
period) and the prevalence (number of people affected at any one
time) are also compiled in these studies.
 Case-control studies and
cohort studies are two types
of analytical studies that can
be used:
Case-control studies
compare people with the disease
(case) to people without the
disease (control) and look for
differences in exposure to the
possible causes of the disease.
A case-control study, set up in
London in 1947 by Richard
Doll, compared patients with
lung cancer to patients with
other conditions. Information
about many factors in their life,
including their smoking habits,
was collected. The results of this
study showed that most of the
individuals with lung cancer
were smokers and suggested a
link between smoking and lung
Cohort studies involve studying two or more similar groups of
people who are free of the disease. These groups differ in one main
factor, that being their exposure to the potential cause of the
These groups are followed over a
long period of time to compare
the resulting incidence of the
disease that is being studied. For
example, after the 1947 casecontrol study that established a
link between smoking and lung
cancer, a cohort study was set up
in England in 1951 by A. B. Hill.
This study followed more than
40 000 doctors over a 10-year
period. One group of doctors were
smokers (the test group) and the
other group were non-smokers (the
control group). At the end of the
study it was found that the test
group had a much higher incidence
of lung cancer than the control
group. This study also revealed that
the greater the number of cigarettes
smoked daily, the greater the chance
of dying from lung cancer.
3. Intervention studies are used
to test the effectiveness of a
treatment (e.g. a clinical trial of a
new drug), or the effectiveness of a
public health campaign to change
the behaviour of the population as a
whole in order to decrease the
incidence of the disease. For
example, the effectiveness of
campaigns such as the ‘Quit’
campaign to decrease the number
of people smoking is evaluated
using a study such as this.
Epidemiological Studies
Epidemiological studies should:
 be conducted over a long period of time
 study very large sample sizes (thousands)
 collect a range of relevant data from a large group of both
affected and unaffected people (case-control). This relevant data
could include age, sex, diet, occupation, lifestyle and exercise
Epidemiological Studies
 have participants that
represent a broad range of
society and lifestyles
 use control groups who are
not exposed to the potential
cause of disease but are similar
in all other respects to the test
group (cohort studies)
 collect data on the incidence,
prevalence, mortality and
morbidity rates of the disease
being studied
Epidemiological Studies
 statistically analyse the data to
identify patterns and trends in
the occurrence of the disease
 identify the possible cause of the
disease and any risk factors
 develop a management plan
with strategies to control or
eliminate the disease and
educate the public
 evaluate the effectiveness of
control and treatment
-Students to complete Smoking and Lung Cancer Activity

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