Research Methods
Alemu T.
09/17/21
Research Methods
The methods of a research project is the core of
the study.
The
following are important questions to
consider when beginning to prepare a research
design for a research proposal.
2
Research Methods …
What do I want to measure?
 How can I measure it?
 Where should I measure it?
 What will I do with the answers collected?
 How can I check whether my methods for measuring
are correct before beginning a large study?
 What professional and non-professional staff do I
need to carry out this study?
 What types of logistical support do I need?
 Are there any ethical problems related to the study?
 How can I avoid introducing biases into the study?
 What constraints may affect this study?
3
Components of a research design that should be
addressed in the method section:
 Study
area,
Study
period,
Study
design,
Population, Sample size determination and
sampling procedures, Variables, Data collection,
Data
processing
and
analysis,
Ethical
considerations, Data quality assurance, and
Operational definitions
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Study area
Location, Physical features (climate,
altitude...), Population size and
composition
Infrastructures -education, health,
communication…
Economy
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Study period
Time required to conduct the study
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Study Design
A study design is the process that guides
researchers on how to collect, analyze and
interpret observations.
It
is a logical model that guides the
investigator in the various stages of the
research.
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Selection of study design depends
on:

State of knowledge

Type of information you want to obtain

The nature of the problem

The resources available

personal experience

Audience
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Selection of study design depends
on …
The
knowledge and creativity of the
researcher
Sample to be taken
Purpose of the research
Access of study subject.
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1) the research problem
Research problems
approaches
call
for
specific
E.g. If the problems calls for:
a) the identification of factors that influence
an outcome
b) the utility of an intervention, or
c) knowing the prevalence of diseases
Then a quantitative approach is best
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The research problem …
If a concept or phenomenon needs to be
understood because little research has
been done on it,
Qualitative approach is preferred
 Qualitative research is exploratory and is useful
when the researcher does not know the
important variables to examine
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Types of study design
Non-intervention (Observational studies):
◦ in which the researcher just observes and
analyses researchable objects or situations but
does not intervene;
Intervention studies
◦ in which the researcher manipulates objects or
situations and measures the outcome of his
manipulations (e.g., by implementing intensive
health education and measuring the improvement
in immunization rates.)
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Study designs could be
Exploratory/fact finding
Descriptive
Analytical/ explanatory
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Exploratory studies
An exploratory study is a small-scale study of
relatively short duration, which is carried out
when little is known about a situation or a
problem.
It is used to gain initial insight
It
may include description as well as
comparison.
E.g.-assessment of needs of HIV patients on
ART using in-depth interview
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Descriptive studies
document the magnitude, distribution and
trends over time
Purpose: To characterize the amount and
distribution of disease and other health
related conditions within a population.
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Cont’d
Descriptive studies generally precede
analytic studies designed to investigate
determinants of disease.
Thus, descriptive studies often help to
generate research hypotheses.
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Designing descriptive studies
Defining a population of interest
 Recruiting a representative sample

Measuring the health characteristic of
interest
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Descriptive Study Designs
• INDIVIDUALS level
 Case reports
 Case series
 Cross sectional surveys
POPULATIONS (GROUPS)
◦ Ecologic (aggregate) studies
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Case Reports
Case Report?
a
careful, detailed report by one or more
clinicians of the profile of a single patient.
◦ One of the first steps in outbreak investigation
◦ Often useful for hypothesis generating and
examining new diseases, but conclusions about
etiology cannot be made.
Strengths- useful for hypothesis generation.
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Case report …
Limitations:
• No appropriate comparison group
• Cannot be used to test for presence of a valid
statistical association
• Since based on the experience of one person:
 presence of any risk factor maybe purely coincidental
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Case Series
Case series ?
 Collection
of individual case reports
occurring within a fairly short period of
time.
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Case series …
Strengths:
• Used as an early means to identify the
beginning or presence of an epidemic.
• Can suggest the emergence of a new
disease (i.e. AIDS)
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Case series …
Limitations:
• Lack of an appropriate comparison group
• Cannot be used to test for presence of a
valid statistical association
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Correlational/ecological studies?
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Ecological studies
Does not provide individual data
presents
average exposure level in the
community
Examples, hypertension rates and average
per capita salt consumption in two
communities
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Cont’d
Strengths- it is quick, inexpensive and
often uses available data
Limitations -inability to link exposure
with disease outcome at individual level
◦ lack of ability to control for effects of
potential confounding factors
◦ it may mask a non-linear relationship between
exposure and disease.
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A cross-sectional study (survey)
A cross-sectional study?
Snapshot
of the health status of
populations at a certain point in time.
Compare prevalence of disease in persons
with and without the exposure of interest
Cross-sectional studies must be done on
representative samples of the population.
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Advantage of Cross-sectional
Provides prevalence estimates of exposure
and disease.
Easier to perform than studies that require
follow-up (hence relatively inexpensive).
Can evaluate multiple risk (and protective)
factors and health outcomes at the same point
in time
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Advantage …
May identify groups of persons at high or
low risk of disease
• Can be used to generate hypotheses about
associations between predictive factors
and disease outcomes
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Limitation of cross-sectional
Temporal sequence between exposure
and disease cannot be established
* i.e. chicken-or-egg dilemma.
Example: In the study of knowledge of
modern contraceptive, did the women
know about it and then start to use it or
did they learn about it because they were
using it.
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Explanatory /Analytical studies
Analytical studies?
At least two variables must be specified
in advance, an exposure and a disease or
health state
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Types of analytical study designs
Observational studies
Interventional study
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Comparative cross-sectional
Example-a survey on malnutrition may wish
to establish:
The percentage of malnourished children in a
certain population;
Socio-economic, physical, political variables
Feeding practices; and
The knowledge, beliefs, opinions
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Cont’d
he
will try to determine which socioeconomic,
behavioral
and
other
independent
variables
may
have
contributed to malnutrition.
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Case-control study design
Case-control study design?
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Case-control…
exposed
cases
Not exposed
Study pop
exposed
Not exposed
controls
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Study begins here
Selection of cases
A/ Definition- precise definition of cases(clinical,
laboratory and other criteria
B/ Inclusion and exclusion criteria
-cases should be selected to improve validity(ex.
By excluding cases with coexisting disease)
-cases should be restricted to limited time period
and geographic area, age range etc…
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Sources of cases
Hospital (health institution) cases
◦ easy and inexpensive to conduct but prone to
selection bias
Population (community) based cases
◦ avoid selection bias
◦ allows the description of disease in the entire
population
◦ expensive
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Selection of controls
Consider
◦ comparability with cases
◦ practicability
◦ economic impact
Controls and cases should came from the
same source population
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Cont’d
The
prevalence of exposure among
controls should reflect the prevalence of
exposure in the source population.
The time during which a subject is eligible
to be a control should be the time in which
the individual is also eligible to be a case.
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Sources of controls
Hospital (health institution) controls
Advantages
Easily identified and readily available
Less expensive
More likely than healthy individuals to be
aware of antecedent exposure or events.
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Cont’d
Disadvantages
They are different from healthy people in
many ways
Studies demonstrated that hospitalized
patients are more likely to have the
experience of exposure
A true association might be masked
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Cont’d
General population controls
Advantages
Are generally healthy
Reflect well the population living in the
area
Generalizability is possible
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Cont’d
Disadvantages
Are expensive and time consuming
May not remember exposure status
because of less concern
Less motivated to participate
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Cont’d
Special controls
Special controls are individuals
related to the case in some way
like friends, household members,
neighbor, siblings etc
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Cont’d
Advantages
They are healthy
More likely to be cooperative
Offer a degree of control over some
confounding factors such as ethnicity,
socio-economic status, environmental
factors etc
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Cont’d
Disadvantages
If the study is likely to be similar to
that of the cases, an underestimate of
the true effect may result.
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Cont’d
Sources of exposure data (cases and
controls):
Study subjects (self-report).
Records (preferably completed before the
occurrence of outcome events).
Interviews with surrogates (spouses,
siblings, etc.).
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Measure of association in case controls study
 The measure of association in case control study is
Odds Ratio(OR)
OR
=
odds of disease in exposed
odds of disease in unexposed
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Measure of association…con
Odds = the chances of something happening
the chances of it not happening
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Measure of association…cont
OR= ad/bc
OR=1=Null hypothesis
OR>1 Exposure is a risk factor
OR<1 Exposure is protective
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Advantages of case-control study
Quick and inexpensive
Relatively simple to carryout
Optimal
for the evaluation of rare
diseases
Can examine multiple etiologic factors
for a single disease
Well suited for the evaluation of disease
with long latent period
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Limitations of case-control study
Inefficient
for the evaluation of rare
exposure
Cannot directly compute incidence rates
of diseases
Difficult
to
establish
temporal
relationships
Prone to selection and recall bias
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Cohort study design
Cohort?
◦ E.g. Birth cohorts, cohort of smokers, occupational
exposures
Cohort study design
subjects are defined according to their
exposure status
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Cont’d
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Types
Closed vs. Open
◦ Closed cohort: exposure groups are defined at
the start of follow-up and no new members are
added during the follow-up
◦ Open/dynamic cohort: people move in and out
the study
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Cont’d
Incidence cohort vs. Prognostic (clinical)
◦ Incidence Cohort Study
 To assess incidence of disease
 To identify risk factors for disease onset
 Incidence greater in exposed than non-exposed?
◦ Prognostic Cohort Study
 Follow diseased cohort to assess factors associated
with outcome (recovery or death)
 Goal is to identify explanatory/prognostic factors of
those factors helped to the dev’t of the disease.
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Prospective vs. Retrospective (Concurrent vs.
Non-concurrent)
Prospective cohort- Healthy cohort (free of the
disease) assembled and followed. More reliable
than retrospective
Retrospective (historical) cohort- the study is
initiated at a point in time after both the exposure
and disease have already occurred.
 It is constructed retrospectively through existing
records
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Cont’d
Can be conducted more quickly and
cheaply
◦ All relevant events have occurred
◦ Efficient for disease with long latency periods
Depend on availability of routine data
◦ Incompleteness
◦ Lack of data on confounding variables
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Selection of exposed group
The
frequency of the exposure in the study
population
The need for obtaining complete and accurate
information
The easiness to collect relevant information and
to follow up
The ability of obtaining sufficient exposed
individuals in a reasonable period of time
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Selection of non- exposed
◦Similar to exposed
◦Control for confounding
factors
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Exposure ascertainment:
• Using pre-existing records
• Conducting
interviews
questionnaire
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and
filling
Outcome ascertainment
Possible sources are routine surveillance,
death
certificate,
periodic
health
examination, hospital records and autopsy
records.
have affirmed outcome criteria and
standard diagnostic procedures applicable
for exposed and non- exposed groups.
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Measures of association in Cohort Studies
Diseased
Exposed
Not
Exposed
Not
Incidence Rates of
Disease Total
Disease
a
b
a+b
a/a + b
c
d
c+d
c/c + d
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Cont’d
Relative Risk (RR) = Iexp / Inon-exp
= [a/(a+b)] / [c/(c+d)]
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Advantages of cohort study:
Valuable for rare exposures
Examines
multiple effects of a single
exposure
Can elucidate temporal relations
Allows direct measurement of risk
Minimize bias in ascertainment
exposure
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of
Limitations of cohort study
Inefficient in evaluation of rare diseases
Expensive
Time consuming
Incompleteness of records
Losses to follow up create problem- leads
to bias
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Interventional studies
The researcher manipulates a situation
and measures the effects of this
manipulation.
Usually (but not always) two groups are
compared
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Two categories of intervention
studies
Experimental studies and
Quasi-experimental studies.
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Experimental studies
Experimental design is the gold standard
study design
It differs from other study designs
◦ The investigator has full control in
administering the factor of interest
◦ Random assignment or allocation of both
study and control subjects
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Classification of experimental
studies
Classification based on the population studied:
◦ Clinical trial- usually in clinical settings and
subjects are patients
◦ Field trial- used in testing drug for preventive
purpose. e.g. vaccine trial
◦ Community trial- unit of the study are group
of people/ community e.g. fluoridation of
water to prevent dental caries
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Quasi-experimental studies
either randomization or control group is
missing however, always includes the
manipulation of an independent variable
which is the intervention. Types
uses two (or more) groups
uses only one group ( ‘BEFOREAFTER’ study)
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Problems related to intervention
studies
Ethical issues:
◦ Practices or substances already known to be
harmful should not be used
◦ Therapies known to be beneficial should not be
withheld from any affected person
◦ Investigators have to have a complete
knowledge of the study subjects
◦ The researcher must have informed consent
from each of study subjects
◦ A written research protocol is a must
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Cont’d
Feasibility or practical issues:
Cost
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Thank you
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