1. MBBS.USMLE, DPH, Dip-Card, M.Phil, FCPS
Professor Community Medicine
Gujranwala Medical College Gujranwala
Ex-Professor Community Medicine
UmulQurrah University Makka/King Khalid
University Saudi Arabia
DR Muhammad Tauseef Javed
5/31/2023 1

2. 5/31/2023 DR M TAUSEEF JAVED 2
Study designs in
epidemiology

3. Components of Epidemiology
 Measure disease frequency
 Quantify disease
 Assess distribution of disease
 Who is getting disease?
 Where is disease occurring?
 When is disease occurring?
 Formulation of hypotheses concerning causal
and preventive factors
 Identify determinants of disease
 Hypotheses are tested using epidemiologic
studies

4. Basic Research Study
Designs and their
Application to Epidemiology

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Why we need research design
Classification of epidemiological
research and study designs
Characteristics of each study design
Choosing appropriate study design for
research title under consideration
What will you learn in this
session?

6. Big Picture
 To prevent and control disease
 In a coordinated plan, look to
 identify hypotheses on what is
related to disease and may be
causing it
 formally test these hypotheses
• Study designs direct how the
investigation is conducted

7. Study design: Definition
A study design is a specific plan
or protocol for conducting the
study, which allows the
investigator to translate the
conceptual hypothesis into an
operational one.

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Study design
A set of defined steps required to
carry out research on a problem
under study. The design will define:
 How study subject are selected?
 Method of sample size estimation
 Procedure of data collection
 Procedure of data analysis
 Types of statistical test required

9. Comparison (I)
Qualitative
 Understanding
 Interview/observation
 Discovering frameworks
 Textual (words)
 Theory generating
 Quality of informant more
important than sample size
 Subjective
 Embedded knowledge
 Models of analysis: fidelity
to text or words of
interviewees
Quantitative
 Prediction
 Survey/questionnaires
 Existing frameworks
 Numerical
 Theory testing (experimental)
 Sample size core issue in
reliability of data
 Objective
 Public
 Model of analysis:parametric,
non-parametric

10. Comparison (II)
Quantitative
 Methods
 Observational
 Experimental
 Mixed
 Sampling: Random
(simple, stratified,
cluster, etc) or
purposive
 Quality Assurance:
 Reliability: Internal and
External
 Validity: Construct,
Content, Face
Qualitative
 Methods
 Focus Groups
 Interviews
 Surveys
 Self-reports
 Observations
 Document analysis
 Sampling: Purposive
 Quality Assurance:
 Trustworthiness:
Credibility,
Confirmability,
Dependability,
Transferability
 Authenticity: Fairness,
Ontological, Educative,
Tactical, Catalytic

11. Case report
Case series
Descriptive
Epidemiology
Descriptive
RCT
Before-After
study
Cross-sectional
study
Case-Crossover
study
Case-Control
study
Cohort study
Analytic
Ecologic study

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Classification of Epidemiological
Research
Descriptive
Research
Analytic
Research
Observational
Analytic Studies
Experimental
Analytic Studies

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Objectives at various levels
DESCRIPTIVE STUDIES
1. Knowing the frequency of disease
2. Knowing the distribution
3. Developing the hypothesis
OBSERVATIONAL
ANALYTICAL
1. Testing the hypothesis
2. Establishing association
EXPERIMENTAL OR
INTERVENTIONAL STUDIES
1. Strengthening association
2. Establishing the cause
Study Types Objectives

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Design Strategies in Epidemiological
Research
DESCRIPTIVE STUDIES
1. Cross-sectional studies
2. Population Correlations
3. Case reports
OBSERVATIONAL
ANALYTICAL
1. Cross-sectional studies
2. Case control study designs
3. Cohort study design
EXPERIMENTAL OR
INTERVENTIONAL STUDIES
1. Therapeutic or drug trials
2. Preventive trials
Classification Study designs

15. Timeframe of Studies
 Prospective Study - looks forward,
looks to the future, examines future
events, follows a condition,
concern or disease into the future
time
Study begins here

16. Timeframe of Studies
 Retrospective Study - “to look
back”, looks back in time to study
events that have already occurred
time
Study begins here

17. Study Design Sequence
Case reports Case series
Descriptive
epidemiology
Analytic
epidemiology
Clinical
trials
Animal
study
Lab
study
Cohort Case-
control
Cross-
sectional
Hypothesis formation
Hypothesis testing

18. Descriptive Studies
Case-control Studies
Cohort Studies
Develop
hypothesis
Investigate it’s
relationship to
outcomes
Define it’s meaning
with exposures
Clinical trials
Test link
experimentally
Increasing
Knowledge
of
Disease/Exposure

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Assessment of disease profile
among the school children
Study of Immunization Status in
children under 5 years
Evaluation of blood glucose and
cholesterol levels in obese
Prevalence of hepatitis B and C
among in high risk groups
Descriptive study statements

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1. Defining the problem under study
2. Defining the population under study
(Concept of denominator)
3. Taking the sample of population
4. Collecting the Data
5. Analyzing interpretation of data
6. Drawing the conclusion
7. Generation of hypothesis
Steps for descriptive research

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1. Theoretical definitions
2. Clinical definitions
3. Provisional diagnosis
4. Laboratory diagnosis
What are Operational Definitions
 What is the case definition of tuberculosis?
 What is the case definition of Hepatitis B?
Defining the problem under
study

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Defining the population under study
 Geographical bound population
 Age specific population
 Disease specific population
 Occupation specific population
 Hospitalized patients
 Vaccinated un-vaccinated
 Male or Female population

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Data Collection Procedure
1. Development of data collection
forms or questionnaire
2. Interview
3. Recording observation /clinical
examinations
4. Examination of records

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Primary and Secondary Data
Data specifically collected for the
problem under study is primary data
Using already collected data or other
data sources for research purpose

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Primary Data
Merits Demerits
1. Data forms are objectively
designed
2. No chances of missing
information's
3. Data is uniform
4. Data is easy to analyze
5. Data is valid hence
research is valid
1. Data is not readily
available
2. Cost and logistics
3. Data collection is time-
consuming

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Secondary Data Sources
 Census data
 Birth and death records
 Clinical records
 Employment records
 HMIS data
 Surveys

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Secondary Data
Merits Demerits
1. Readily available data
2. Saving of time in data
collection
3. Saving the cost of data
collection
1. Data is not objectively
collected
2. Required information may
be missing
3. Data is not uniform
4. Poor quality data
5. Difficult to analyze
6. Data is less valid hence
research is less valid

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Data Analysis
 Finding the frequency
 Finding the percentages
 Tabulation
 Graphical presentation

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Frequency Distribution
Scabies Frequency Percentage
Urban 20 20.00
Slums 56 56.00
Rural 24 24.00
Total 100 100.00%
Dr. M. Ashraf Majrooh

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Arranging the data by person,place
and time
 Frequency among male & female
 Frequency among white & black
 Frequency among rural & urban
 Frequency in Asia & Europe
 Frequency in winter & summer
 Month-wise frequencies
 Year-wise frequencies

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Drawing the conclusion
 Frequency is more in male than
female
 Frequency is more in urban or rural
 Frequency is more in winter than
summer

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Hypothesis Formulation
 Method of difference
Difference of frequencies in two sets of
circumstances
 Method of agreement
A single factor is common in number
circumstances in which disease occurs
with high frequencies
 Method of Concomitant variations
Frequency of factor varies with frequency of
disease

33. Case Reports
 Detailed presentation of a single
case or handful of cases
 Generally report a new or unique
finding
 e.g. previous undescribed disease
 e.g. unexpected link between
diseases
 e.g. unexpected new therapeutic
effect

34. Case Series
 Experience of a group of patients
with a similar diagnosis
 Assesses prevalent disease
 Cases may be identified from a
single or multiple sources
 Generally report on new/unique
condition
 May be only realistic design for rare
disorders

35. Case Series
 Advantages
 Useful for hypothesis generation
 Informative for very rare disease with
few established risk factors
 Characterizes averages for disorder
 Disadvantages
 Cannot study cause and effect
relationships
 Cannot assess disease frequency

36. Case Report
Case Series
Descriptive
Epidemiology Study
One case of unusual
findings
Multiple cases of
findings
Population-based
cases with denominator

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 The population is examined in single point of time
or it is snap-short of the situation
 Both the exposure and the disease are assessed
at the same time
 Population as whole or representative sample of
the population is studied
 The studies are unable to explain the time
association of the disease
 These studies are less time consuming as
compared to longitudinal studies
 Important cross-sectional surveys in Pakistan
were, PIHS, MICS, PDS etc.
Salient features of cross-
sectional studies

38. Thanks for your kind
attention
and listening

39. Analytical Research
Observational Analytical
Research
Experimental / Interventional
Analytical Research
Investigator simply observe
the effects of natural exposures
among the study subjects
(Used for hypothesis testing)
Investigator himself do some
intervention and analyze the
effects among study subjects
(Used for hypothesis testing)
Cohort Studies
Case Control Studies
Clinical interventional
Interventional studies
Preventive interventional
studies
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DR M TAUSEEF JAVED

40. Study Designs -
Analytic Epidemiology
 Experimental Studies
 Randomized controlled clinical trials
 Community trials
 Observational Studies
 Group data
 Ecologic
 Individual data
 Cross-sectional
 Cohort
 Case-control
 Case-crossover

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Observational Analytic
Study Designs
1. Cohort Study design
2. Case Control Study design

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What is cohort?
A group of people sharing a common
event or characteristic
The name of the cohort is given on the
basis of event the people share
 Birth cohort
 Enrolment cohort
 Atomic explosion cohort
 Occupational cohorts

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Consider the following
statements
 Hypertension is more common
among the obese persons?
 Physical activity is protective factor
against CHD?
 Ionizing radiation causes blood
cancer, infertility, congenital
anomalies?

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Cohort Study design
Compare
Non Exposed
group
Disease Present
Disease absent
Exposed group
Disease Present
Disease absent
Select
Cohort study proceed from cause to the effect
Follow up

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Steps of Cohort Study
1. Selection of exposed population
2. Selection of comparison group
3. Defining and measuring of
exposure
4. Follow-up of both groups
5. Assessment of outcome (Effects)
6. Analysis
7. Scope and limitations

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Selection of Exposed
Population
 What do you mean by exposure?
 Give some examples of exposures?

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Exposure Groups
Same population is segregated between
exposed and non exposed groups
♣ Smokers and non-smokers
♣ Diabetic verses non- diabetic
♣ Active verses sedentary workers
♣ Special exposure groups
♣ Rubber processing
♣ Uranium mining, coal-mining

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Exposure Groups
Comparison within the same population
with different levels of exposures
 Non-smokers
 Casual smokers
 Regular smokers
 Chain smokers
Multiple Comparison groups

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Sources of exposure
information
 Information from records
 Interview of cohort members
 Medical examination
 Biochemical assessment
 Information and measurement from
environment

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Categorization of exposure
status
 Length of employment e.g. 5,10,15, years
 Numbers of cigarette per day
 Distance from the source
 Biological levels of exposure, cholesterol
level, blood sugar level, blood pressure
 Environmental levels, Chemical levels,
Radiation levels

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Assessment and measurement of
outcome or effect of exposure
Effect with fatal
outcome
 Medical certificate
 Hospital records
 Physician autopsy
 Visual certainty
 Postmortem
Non-fatal outcome
 Physician records
 Hospital records
 Discharge certificates
 Special registrations
 Pathological reports
 Periodic medical
examination of cohort

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Analysis of Cohort study
♣ Disease Rate or Incidence among the exposed
♣ Disease Rate or Incidence among the non-
exposed
RELATIVE RISK (Risk Ratio)
Incidence of disease among the exposed
(having the risk factor)
Incidence among the non-exposed
(not having the risk factor)
Relative Risk =

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Interpretation of Relative Risk
 What do you understand by RR= 1 ?
 What do you understand by RR= 3 ?
 What is your opinion if RR is less
than 1

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Scope of cohort study design
 It is important to study the rare exposures
 Can examine multiple effect of a single
exposure
 Can elucidate time relationship between
exposure and the disease
 Allows direct measurement of incidence of
disease in exposed and non-exposed
group

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Limitations
 Is inefficient design for evaluation of
rare diseases
 If prospective it is extremely
expensive and time consuming
 If retrospective it requires the
availability of adequate records

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Case Control Study design
Non-diseased
Exposure Present
Exposure absent
Diseased
Exposure Present
Exposure absent
Compare
Case control study proceed from effect to the cause
Select
Trace back

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Case Control Study Steps
1. Definition of cases
2. Selection of cases
3. Selection of Controls
4. Ascertainment of exposure status
5. Analysis
6. Conclusion and interpretation

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Defining the cases
 How will you define poliomyelitis?
 What is acute flaccid paralysis (AFP)
 Is AFP is Poliomyelitis
 What is WHO Criteria of
poliomyelitis?
 Case definition of Tuberculosis
 Cases should be representative of all
diseased

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Selection of Cases
 Preferably new cases or incident
cases
 Prevalent cases (cases already
present)
 Random selection
 Convenient selection

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Control
Control must be Ideally matching
with the cases by age, sex and other
characteristics except the control
must not be suffering from diseases

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Criteria for control
 Marching by all respect with cases
except not having disease
 Hospital controls
 Neighborhoods controls
 Friends and relatives
 Controls from general population

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Methods of selection of control
 Random Selection
 Convenient Selection
 What should be the ratio between
cases and control?

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Ascertainment of Exposure
1. Setting the criteria for exposure
2. Methods of measuring the
exposures
a) Observation
b) Interviews
c) Questionnaire
d) Examination of records

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Analysis
1. Exposure Rates among the
disease (Cases)
2. Exposure Rates among the non-
disease (Control)
3. Odd’s Ratio

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Limitations
 Is an inefficient design for evaluation
of rare exposure
 Incidence rate cannot be computed
 Time relationship cannot be
estimated
 This study design is more prone to
bias

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Scope of case control study design
 It is quick and inexpensive as
compared to other analytic study
designs
 It is particularly suitable for evaluation
of diseases with long latent periods
 It is optimum design for rare diseases

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Experimental Analytic Studies
Experimental analytic are exposure
based and the exposure is introduced
by the Investigator
Objectives
 Scientific proof of etiological or risk factor
 Effectiveness/ efficacy of drugs, vaccine and
health services
 Completion of natural history of disease

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Experimental analytic
research
Randomized
Control Trials
1. Non-randomized
Trials
2. Uncontrolled
Trials
Can you give example of randomized control and
non-randomized trials?

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Steps of experimental /
interventional research
1. Drawing a study protocol
2. Selection of Reference population
3. Selection of Study population
4. Randomization
5. Intervention or Manipulating
6. Follow up
7. Assessment of Outcome
8. Analysis and interpretation of results

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Research protocol?
 A lay down procedure for conduction of
study it addresses the
Design issues
Inclusion criteria and exclusion criteria
Blinding (Single, double, or triple blinding)
Outcome criteria
Duration of follow-up
Ethical issues
Dr. M Ashraf Majrooh

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Reference population?
 The population to which the results
of the study are to be applied
All human being if study is
universally applicable
Geographically bound population
Age specific population
Gender specific population
Other characteristics

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Study population?
 The selected individuals which are
actually enrolled for experimental
study
Eligible population
Eligible but not willing for participation
Eligible and willing for participation
If you lay down some inclusion criteria, the cases
fulfilling that criteria will be eligible
The subject who give consent are the willing subjects

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Experimental population
potentially eligible
Unwilling
Completed screening Ineligible
Reference Population
Study subjects
(Willing and eligible)

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Grouping and Randomization
1. Experimental Group
2. Control Group
Interventions/treatments are assigned
randomly
Every individual in study population has the
equal probability to go in to experimental and
control groups is the Randomization
Step-4

75. Experimental population
potentially eligible Unwilling
Completed screening Ineligible
Willing and eligible
participants
Reference Population
Control
Group
Experimental
Group
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Study Population
Control
Group
Experimental
Group
Is it Randomization?

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Randomization
Study Population
Control
Group
Experimental
Group

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Advantages of randomization
 To provide the comparability by age sex
and other characteristics
 Prevent potential bias from investigator
side
 Confounding variables are equally
distributed
 Give more authenticity to study

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What is intervention or
manipulation?
 Clinical Trials
 Preventive Trials
 Behavioral modification or risk
factor trials
 Cessation Trials

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Follow up and compliance
 By history and clinical examinations
 Disputable outcomes (Subjective
symptoms) relief of pain,
 Non-disputably out comes
(Systemic findings)

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Ascertainment of outcome
 Positive outcome
If we are looking for beneficial outcome of
and intervention
 Negative Outcome
If we are looking for adverse effects of an
intervention

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Analysis
 Incidence of outcome in experimental
group
 Incidence of outcome in control group
 If incidence of outcome are significantly
more among the experimental group our
hypothesis is correct and vice versa

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RR from 2x2 Table
c
c + d
Incidence
among Control =
a
a + b
Incidence among
experimental group =
a/ a+ b
c / c + d
Relative Risk =

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What is blinding?
 The subjects are not knowing the group
to which they are belonging This is
single blind (It is not possible for every
trial)
 Neither the subject nor doctor is aware
about the groups (Double blind trials)
 The subject, the doctor and the person
doing the analysis are not aware about
the groups in triple blind trials

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Important Issues in experimental
studies
Ethical Issues
Consent Issues
Sufficiently large willing population
required
Maintenance of Compliance
Issues in measurement of outcome
Issues of early termination of trials
Cost Issues

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Ethical Issues in human experiments
 The substance already known to be
harmful are not allowed for exposure
 The therapy which are known to be
beneficial are not be disallowed
 Written consent is required from the
subject to be enrolled for study

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Assignment (Choosing study design)
 Every participant will phrase 5 research
statements
 Participants will be divided in to groups
 Discuss with each other and choose most
suitable study design for each statement
 Give the important steps of selected study
designs
 Presentation from each group

88. Thanks for your kind
attention
and listening

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the difference between relative
risk and odds ratios
 Relative Risk and Odds Ratios are often
confused despite being unique
concepts. Why?
 Well, both measure association
between a binary outcome variable and
a continuous or binary predictor
variable.

90.  The relative risk is confused by some with the
odds ratio and absolute risk. Relative risk is
the ratio of the probability of an event
occurring with an exposure versus the
probability of the event occurring without the
exposure. Thus to calculate the relative risk,
we must know the exposure status of all
individuals (either exposed or not
exposed). This implies that relative risk is only
appropriate for cases where the exposure
status and incidence of disease can be
accurately determined, such as prospective
cohort studies.
5/31/2023 DR M TAUSEEF JAVED 90

91.  Relative Risk and Odds Ratios are often
confused despite being unique
concepts. Why?
 Well, both measure association
between a binary outcome variable and
a continuous or binary predictor
variable.
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98. When Is the Odds Ratio a Good
Estimate of the Relative Risk?
 In a case-control study, only the odds ratio
can be
calculated as a measure of association,
whereas in a
cohort study, either the relative risk or the
odds
ratio is a valid measure of association.
5/31/2023 DR M TAUSEEF JAVED 98

99.  When is the odds ratio (relative odds)
obtained
in a case-control study a good
approximation of the
relative risk in the population? When the
following
three conditions are met:
5/31/2023 DR M TAUSEEF JAVED 99

100.  1. When the cases studied are representative, with
regard to history of exposure, of all people with
the disease in the population from which the
cases were drawn.
2. When the controls studied are representative,
with regard to history of exposure, of all people
without the disease in the population from
which the cases were drawn.
3. When the disease being studied does not occur
frequently.
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