Study Design (Epidemilogical method)

Dr. Animesh Gupta
MD, FDM, FAGE
Associate Professor
Dept. of Community Medicine, NMCH, Jamuhar.
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Dr. Animesh Gupta Study Design (Epidemiological Methods)

▪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
Dr. Animesh Gupta Study Design (Epidemiological Methods) 2

TYPES
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QUANTITATIVE QUALITATIVE

▪Quantitative research is used to quantify the problem by
way of generating numerical data which can be
transformed into useable statistics. It can generalize
results fromsample to population.
▪Qualitative research is exploratory research. It is used to
gain an understanding of underlying reasons,opinions etc.
and provides insight into the problem.
4Dr. Animesh Gupta Study Design (Epidemiological Methods)

▪Descriptive
▪Analytic
▪Experimental
▪Study of the occurrence and
distribution of disease
▪Further studies to determine the
validity of a hypothesis concerning
the occurrence of disease.
▪Deliberate manipulation of the cause
is predictably followed by an
alteration in the effect not due to
chance

OBSERVATIONAL STUDIES
DESCRIPTIVE STUDY ANALYTICAL STUDIES
✓ TIME
✓ PLACE
✓ PERSON
➢ CROSS SECTIONAL STUDY
➢ CASE-CONTROL STUDY
➢ COHORT STUDY
EXPEREMENTAL STUDIES
➢ RANDOMIZED CONTROLLED TRIAL (RCT)

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▪1st phase of an epidemiological investigation
▪ Relatively inexpensive and less time-consuming than
analytic studies, they describe,
▪Patterns of disease occurrence, in terms of,
▪When is the disease occuring – time distribution
▪Where is it occuring – place distribution
▪Who is getting a disease – person distribution

▪ Defining the population to be studied
▪ Defining the disease under study
▪ Describing the disease by
✓ Time
✓ Place
✓ Person
▪ Measurement of disease
▪ Comparing with known indices
▪ Formulation of etiological hypothesis

DESCRIPTIVE Health and disease in the community
What? Who? When? Where?
What are the
health problems
of the
community?
What are the
attributes of
these illnesses?
How many
people
are affected?
What are the
attributes of
affected
persons?
Over what
period of time?
Where do the
affected
people
live, work or
spend leisure
time?

▪Detailed presentation of a single case.
▪Generally report a new or unique finding
✓e.g.previous undescribed disease
✓e.g.unexpected link between diseases
✓e.g.unexpected new therapeutic effect
✓e.g.adverse events

▪Experience of a group of patients with a similar diagnosis
▪Cases may be identified from a single or multiple sources
▪Generally report on new/unique condition
▪Advantages
• Useful for hypothesis generation
• Informative for very rare disease established risk factors

▪Case Report → One case of unusual findings
▪Case Series → Multiple cases of findings

▪Data collected at a singlepoint in time
▪An“observational”design that surveys exposures and
disease status at a single point in time (a cross-section of
the population)
▪Measures prevalence
▪A “Snapshot”

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▪Ancient Roman Military
unit, A band of
warriors.
▪Persons banded
together.
▪Its a group of people
who share a common
characteristic or
experience. [Latin]
▪E.g. age, birth date,

▪ Longitudinal
▪ Prospective studies
▪ Forward looking study
▪ Incidence study
▪ Starts with people free of disease
▪ Assesses exposure at “baseline”
▪ Assesses disease status at “follow-up”

STUDY DESIGN
To examine a relation between a factor and the disease:
❑ All subjects are free from the disease at the beginnning
❑ Subjects are categorised on the basis of presence or
absence of exposure to the risk factor
❑ Subjects are then followed over time to determine who
develops the disease

People
without
the
disease
Exposed
Not
Exposed
Disease
No
Disease
Disease
No Disease

▪Selection of study subjects
▪Obtaining data on exposure
▪Selection of comparison group
▪Follow up
▪Analysis

▪Calculation of incidence rates among exposed and non
exposed groups
▪Estimation of risk

INCIDENCE RATES OF OUTCOME
a b a+b
c d c+d
a+c b+d TOTAL
EXPOSURE
STATUS
DISEASE STATUS
TOTAL
STUDY COHORT
COMPARISON COHORT
YES
NO
YES NO
❑ Incidence among exposed = a/ (a+b)
❑ Incidence among non exposed = c/ (c+d)

RELATIVE RISK
❑ It is the ratio of the incidence of disease in exposed
compared to incidence in non exposed
❑ RR=
incidence among exposed
incidence among non exposed

INTERPRETATION
▪If RR=1.0, then there is no association between the
exposure and the disease
▪If RR>1.0, then there is positive association between the
agent and disease
▪If RR<1.0, then there is negative association, which means a
curative effect of the agent on the risk of disease. Eg:
immunisation lowers the risk of disease.

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▪ Also knowns as “retrospective study”
▪ From effect to cause
▪ The case control method has three distinct features:
▪ Both exposure and out come have occurred before the start of
the study.
▪ The study proceeds backwards from effect to cause.
▪ It uses a control or comparison group to support or refute
an inference.

1. Selection of cases and controls
2. Matching
3. Measurement of exposure
4. Analysis & interpretation

▪ Matching (matching is the process of selecting controls who
are similar to the cases in certain key characteristics – eg.
age,sex,race)
▪ Individual matching (matched pair)
▪ for each case, a control is selected who is similar to the case for
a given variable
▪ Group matching (frequency matching)
▪ proportion of controls with a given characteristic (variable) is
identical to proportion of cases with the same characteristic

Cases Controls
Risk factor + a b
Risk factor -- c d

▪Odds = is the ratio of the probability that an event will
happen to the probability that it will not happen

▪Odds of exposure among diseased = a/c
▪Odds of exposure among non-diseased = b/d
▪Exposure Odds ratio = a/c ÷ b/d
▪Odds ratio = ad/bc

Case-control study
Individuals with
particular disease (cases)
Individuals without
particular disease (controls)
-------------------------------
Individuals exposed to
particular factor
Individuals unexposed to
particular factor
Cohort study
Presence
or
Absence
of disease
Factor
present
or
absent

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▪ In the 18th century, Scottish surgeon
named James Lind began to unravel
the secrets of scurvy.
▪ While working as naval surgeon (after
eight weeks at sea), he encountered a
cases of scurvy among sailors, and then
he decided to test his idea that the
putrefaction of the body caused by the
disease could be prevented with
acids.
▪ On May 20, he divided the 12 sick
sailors into 6 pairs, and provided each
of them with a different supplement in
their diet.
October 4, 1716 – July 13, 1794

▪Experimental study
▪Basic steps
1. Drawing up a protocol
2. Selecting reference & experimental populations
3. Randomization
4. Manipulation or intervention
5. Follow-up
6. Assessment of outcome

▪ Aims and objectives of study
▪ Questions to be answered
▪ Criteria for the selection of study and control groups
▪ Size of the sample
▪ Procedures for allocation of subjects into study and control groups
▪ Treatments to be applied-when and where and how to what kind of
patients
▪ Standardization of working procedures and schedules as well as
responsibilities of parties involved in trial
▪ Evaluation of outcome of the study

a) Reference or target population
• Is the one to which the findings of the trial ,if found
successful are expected to be applicable.(e.g. drug,
vaccine)
• Can be broad as mankind, or geographically limited or
limited to persons in specific age, sex, occupatinal or social
groups(whole city, school children, industrial workers etc)

b) Experimental or study population
-Derived from the reference population
-Participants of the experimental study
-Randomly chosen
-Chose a stable population (avoid losses to
follow-up)

1. Must give “informed consent” i.e. they must agree to
participate in trial after been fully informed about
purpose ,procedures and possible dangers of trial
2. Representatives of population to which they belong .
3. Qualified or eligible for the trial

▪Participants are allocated into “study” and “control”
groups.
▪Eliminate “bias” and allow comparability
▪Investigator has no control over allocation
▪Individual has equal chance of being in either of the groups

▪ Deliberate application or withdrawal or reduction of the
suspected causal factor to the experimental group(drug,
vaccine, dietary component or habit)
▪ Creates an independent variable (drug or vaccine) effect of
which determined by final outcome that is dependent
variable (incidence of disease, survival time, recovery
period)

▪Examination of both groups till final assessment of the
outcome
▪Attrition : Losses to follow-up due to death, migration or
loss of interest
(difficult to generalize the results of study to reference
population)

▪ POSITIVE RESULTS
Benefits of the experimental
measure such as reduced
incidence or severity of
disease, cost to health service
or other appropriate outcomes
▪ NEGATIVE RESULTS
Severity and frequency of side-
effects and complication if any
including death
Incidence of positive and negative results are compared in both
groups and differences if any are tested for statistical significance

Objective Study type
Prevalence Cross Sectional
Incidence Cohort Study
Causal association Case control
Cohort Study
Prognosis Cohort Study
Natural history of disease Cohort
Treatment effect RCT

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Study Design (Epidemilogical method)

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