2. When you have studied this session, you should be able
to:
• Define and use correctly all of the key words printed in
bold.
• Identify and define appropriate study populations for a
specific type of research study.
• Identify the study variables in descriptions of small-
scale research projects presented to you
• Describe the three survey designs most commonly used
in small-scale health research and comment on their
relative advantages and disadvantages.
3. What is the study population?
• I is the total members of a defined class of
people, objects, places or events selected
because they are relevant to your research
question.
• For example if you want to study maternal
health care the study population
would be all the pregnant women who are
under your care.
4. Variables in health research
• A variable may be in the form of numbers (such
as weight or age), or non-numerical
characteristics (such as occupation, ethnicity,
education level or gender).
• It can be acharacteristic of a person, object, place,
event or phenomenon
• Variables may take numerical (quantitative) or
non-numerical (qualitative) values.
5. Types of study design
• It can be observational (in which the
researcher simply observes what is going on),
or experimental (in which the researcher
intervenes in some way and then observes
what happens as a result)
6. Observational study design
• You just observe and analyze your study subjects or
situations in their natural condition, but the researcher
does not intervene in any way.
• However, the observations should not just be a
haphazard collection of facts; observational studies
should apply the same rigour as experimental
studies by recording the observations in a systematic
way that can lead to meaningful interpretations.
• You are more likely to be involved in observational
studies than in experimental studies.
7. Experimental study
• It is a type of research design in which some of the
conditions are under the direct control of the researcher.
• He or she intentionally alters one or more factors (e.g.
the behavior of participants, or their circumstances and
situations), and then measures the outcomes to analyze
the effects of the alteration.
• For example, you could implement a health education
campaign on the benefits of immunization (this is the
intervention), and then measure any improvement in
immunization coverage rates (by analysing the
outcomes of your intervention).
8. Types of observational studies
• As a Health Extension Practitioner you will
probably only be directly concerned with
observational studies.
• These generally take the form of sample surveys
(of selected individuals) or population surveys
(covering everyone in the population), where the
sample or the population is observed for various
characteristics.
9. Cont
• The most common type of study design you will
be involved in is the observational survey, in
which information is systematically collected
from your study population on a specific topic.
cross-sectional study
case-control study
cohort study.
10. Cross-sectional studies
• You would collect information about the
current situation.
• Therefore, in cross-sectional studies the
information on the possible cause and the
possible effect is collected at the same time.
11. Case-control studies
• You begin by selecting two groups for
comparison: one group of the population (the
cases) who have a characteristic that you wish to
investigate (such as mothers whose child died
within one month of birth, or children with
malnutrition) , and another group (the controls)
where that problem is absent.
• The aim of a case control study is to find out what
factors have contributed to the problem under
investigation.
12. Cohort studies
• The term cohort describes a specific group of people who
are all in a particular situation during a certain period of
time,
• If these people are studied over a long period of time to see
what diseases they develop, this is called a cohort study.
• The most common type of cohort study begins with a
population who share the same general characteristics but
then compares those individuals in the cohort who are
exposed to a disease risk factor (e.g. the tobacco smokers)
with those individuals in the cohort who are not exposed to
the risk factor (in this example, the non-smokers).
• Then you follow everyone in the cohort over a period of
months or years, and compare the occurrence of the
problem that you expect to be related to the risk factor (for
example, lung cancer or pneumonia) in the two groups.
13. Selecting the appropriate study type to
investigate a particular problem
The choice of your study design may depend on
the following factors:
type of problem
knowledge already available about the
problem
resources available for the study
