7/30/2019 Epidemiological Study Methods
1/38
EPIDEMIOLOGICAL
STUDY METHODS
OKETADE SOA
7/30/2019 Epidemiological Study Methods
2/38
OUTLINE
INTRODUCTION
DEFINITIONS CLASSIFICATION
STUDY DESIGNS
VARIOUS DESIGNS CONCLUSION
7/30/2019 Epidemiological Study Methods
3/38
INTRODUCTION
The science of epidemiology has matured
significantly from the times of Hippocratesand john snow [physician] that the
techniques for analysing data vary depending
on the type of dxs being monitored but eachstudy will have similarities. environmental
factors can influence the occurrence of the
diseases.
epidemiology study of what is upon the people
Derived from the greek terms epi=upon,among.
demos=people, district. Logos study, word.
7/30/2019 Epidemiological Study Methods
4/38
DEFINITION OF EPIDEMIOLOGY
Epidemiology is the study of distribution and
determinant of health related state or event in
a specified human population and the
application of this study to the control of healthproblem.
7/30/2019 Epidemiological Study Methods
5/38
EPIDEMIOLOGY [DEFINITION OF KEY TERMS]
Distribution : Frequency (including rates &
risks) & pattern of health events(person,
place, time)
Determinants : factors or events that are
capable of bringing about a change in health
Human population : Epidemiology examines
health events among population groups rather
than individuals.
7/30/2019 Epidemiological Study Methods
6/38
EPIDEMIOLOGY [DEFINITION OF KEY TERMS]
Health related states: infections, chronic
diseases & physiological events &various
states of health such as disability, injury,
mortality
Health related events : immunization, hospital
attendance, bed occupancy
Application : basis for directing interventions
7/30/2019 Epidemiological Study Methods
7/38
CLASSIFICATION
7/30/2019 Epidemiological Study Methods
8/38
CLASSIFICATION(CONT.)
CORRELATIONAL
7/30/2019 Epidemiological Study Methods
9/38
OBSERVATIONAL VS EXPERIMENTAL STUDIES
Observational studies
Allow nature to take its cause; the investigator
measures but does not intervene
Descriptive study: focuses on the description
of the occurrence of a disease in a population
Analytical study analyses relationshipsbetween health status and other variables
7/30/2019 Epidemiological Study Methods
10/38
OBSERVATIONAL VS EXPERIMENTAL STUDIES
Experimental or interventional studies: involve
an active attempt to change a disease
determinant(e.g an exposure or a behaviour)
or the progress of a disaese (through
treatment)
The studies are based on a grp which has had
the experience compared with control grpwhich has not had the experience.
7/30/2019 Epidemiological Study Methods
11/38
PURPOSE OF DESCRIPTIVE
EPIDEMIOLOGY
To generate hypothesis
To permit evaluation of trends in health &
disease and comparisons among countries
and subgroups within countries.
To provide a basis for planning, provision and
evaluation of health services
To identify problems to be studied by
analytical methods and to suggest areas that
may be fruitful for investigation
7/30/2019 Epidemiological Study Methods
12/38
CASE STUDIES(CASE SERIES)
Case reports:documents unusual medicaloccurrence and can represent the first clues tothe formulation of hypothesis, generallyreport a new or unique findings and previousundescribed disease.
Case series: collection of individual case
reports which may occur within a fairly shorttime, and experience of a group of patientswith similar diagnosis.
7/30/2019 Epidemiological Study Methods
13/38
Case Series
AdvantagesUseful for hypothesis generation
Informative for very rare disease with few established
risk factorsUsually of short duration.
Disadvantages
Cannot study cause and effect relationships
Cannot assess disease frequency
9/4/2013 13
7/30/2019 Epidemiological Study Methods
14/38
CROSS-SECTIONAL STUDY
It is also called epidemiologic study or prevalence study
It analyses (describes)data collected on a group ofsubjects at one point in time rather than over a period
of time. i.e they survey exposure and disease at asingle point in time.
Both exposure and outcome variables are beenevaluated at the same point in time(without any inbuiltdirectionality)
Most sophisticated descriptive study
It answers the question WHAT IS HAPPENING RIGHTNOW?
7/30/2019 Epidemiological Study Methods
15/38
QUESTION: WHAT IS HAPPENING?NO DIRECTION OF INQUIRY
o onset time end
subjects
With
outcomeWithout
outcome
7/30/2019 Epidemiological Study Methods
16/38
CROSS-SECTIONAL STUDY
ADV
Best for determining
the status
quo(prevalence) Quick
Relatively inexpensive
DISADV
Only a snapshot at a
time leading to a
misinformation Response rate may be
low ,with result not
representative of the
population
7/30/2019 Epidemiological Study Methods
17/38
Cross-sectional studies
DisadvantagesWeakest observational design,
(it measures prevalence, not incidence of
disease). Prevalent cases are survivorsThe temporal sequence of exposure and effect
may be difficult or impossible to determine
Usually dont know when disease occurredRare events a problem. Quickly emerging
diseases a problem
9/4/2013 17
7/30/2019 Epidemiological Study Methods
18/38
CORRELATIONAL STUDY DESIGN
A study comparing incidence/prevalence of
one event against another on a global scale
Measures that represent characteristics of
entire populations are used to describe the
disease in relation to some factor of interest
(such as age, calendar time, food
consumption, drug use and utilization ofhealth services)
7/30/2019 Epidemiological Study Methods
19/38
CORRELATIONAL STUDY DESIGN
ADV
Compares events amongnations
DISADV
Doesnt compare
individuals, so it might leadto overgeneralization.
7/30/2019 Epidemiological Study Methods
20/38
ANALYTICAL STUDIES
Two basic designs:
Case control or retrospective study
Cohort or prospective
NOTE
There must be a comparison group No control No conclusion(NCNC)
7/30/2019 Epidemiological Study Methods
21/38
CASE CONTROL OR CASE HISTORY
STUDY A group of affected people is compared to unaffected
people(the control)
Its a LONGITUDNAL STUDY (like cohort study) because itsa study over a period of time.
Subjects are selected based on a particular outcome and astudy backwards in time to try to detect the causes or riskfactors that may have earlier been reported in a descriptivestudy
Subjects are then matched and assigned into the two
groups. Subject selected on the basis of disease[e.g lungcancer].
Sometimes called a retrospective study because of thedirection of study
7/30/2019 Epidemiological Study Methods
22/38
CASE CONTROL OR CASE HISTORY
STUDY
7/30/2019 Epidemiological Study Methods
23/38
Advantages of case control
It is relatively easy to carry out bcos we go
back to existing records in the hospital
It is also rapid and inexpensive
It requires comparatively few subjects
It can assist one in studying different
etiological factors
One does not need an ethical clearance
There is no risk to the subject
7/30/2019 Epidemiological Study Methods
24/38
Disadvantages of case control
It introduces bias
To select an appropriate control could be
difficult
It may be difficult to distinguish between the
cause of a disease and an associated factor
7/30/2019 Epidemiological Study Methods
25/38
COHORT STUDY
A cohort is a grp of people who have somethingin common and remain part of a group over anextended time
A group of people exposed to a suspectedetiological agent are compared with a matchedcontrol who have not been similarly exposed.Subject selected on the basis of exposure
[aetiological factor; cigarette smoking] Follow-up over a period to compare the outcome
Also a longitudinal study or prospective study
7/30/2019 Epidemiological Study Methods
26/38
7/30/2019 Epidemiological Study Methods
27/38
ADVANTAGES OF COHORT
There is no bias
The risk can be calculated bcos the incidence
can be calculated
It is effective for studying rare exposures
It allows the study of the natural history of the
disease
It assists in determining the temporal
relationship between the etiological factor &
the disease
7/30/2019 Epidemiological Study Methods
28/38
Disadv of cohort study
It takes a long time
It is expensive
Large no of subjects are needed There could be changes in the standard
methods or diagnostic criteria
7/30/2019 Epidemiological Study Methods
29/38
7/30/2019 Epidemiological Study Methods
30/38
EXPERIMENTAL STUDIES
Studies in which 1 grp is deliberately
subjected to an experience compared with a
control group with no similar experience
The gold standard in medicine bcos it proves
causality
Can be controlled or uncontrolled
7/30/2019 Epidemiological Study Methods
31/38
UNCONTROLLED EXPERIMENTAL
STUDIES
Intervention is not compared with a control
The aim is to confirm that the Intervention
made a difference
7/30/2019 Epidemiological Study Methods
32/38
CONTROLLED EXPERIMENTAL STUDIES
In this study, a drug or procedure is compared
to:
1. Another drug
2. Procedure
3. Placebo
4. Previously accepted tx The aim is to proove the difference due to tx
7/30/2019 Epidemiological Study Methods
33/38
CONTROLLED EXPERIMENTAL STUDIES
Blind trial-single or double
Control could be:
A. METHODOLOGY
1. Concurrent or parallel: randomized or non-
randomized(quasi)
2. Sequential control: self controlled or crossover
3. External control
7/30/2019 Epidemiological Study Methods
34/38
B. STUDY POPULATION
1. Clinical trials
2. Field trials
3. Community trials
7/30/2019 Epidemiological Study Methods
35/38
EXPERIMENTAL STUDIES
ADV
Best study type
Greatest proove of causality
Gold standard for otherdesign
Least bias
Proves best tx or procedure
efficacy
DISADV
Greatest expense
Long duration
Unproven facts adopted bycommunity can hinder
study acceptance
7/30/2019 Epidemiological Study Methods
36/38
overview
7/30/2019 Epidemiological Study Methods
37/38
CONCLUSION
What you cant measure you cant
control!epidemiological study methods are
used to study your health and my health and
its determinants, as we join hands to ensure ahealthier us.
7/30/2019 Epidemiological Study Methods
38/38
THANK YOU
FOR
LISTENING.
Top Related