Transcript 2. Epidemiological Study methods

EPIDEMIOLOGICAL
STUDY METHODS
OKETADE SOA
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OUTLINE
INTRODUCTION
DEFINITIONS
CLASSIFICATION
STUDY DESIGNS
VARIOUS DESIGNS
CONCLUSION
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INTRODUCTION
• The science of epidemiology has matured
significantly from the times of Hippocrates
and john snow [physician] that the
techniques for analysing data vary depending
on the type of dxs being monitored but each
study 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.
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 health
problem.
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.
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
CLASSIFICATION
CLASSIFICATION(CONT.)
CORRELATIONAL
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 relationships
between health status and other variables
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 grp
which has not had the experience.
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
CASE STUDIES(CASE SERIES)
• Case reports:documents unusual medical
occurrence and can represent the first clues to
the formulation of hypothesis, generally
report a new or unique findings and previous
undescribed disease.
• Case series: collection of individual case
reports which may occur within a fairly short
time, and experience of a group of patients
with similar diagnosis.
Case Series
Advantages
 Useful for hypothesis generation
 Informative for very rare disease with few established
risk factors
 Usually of short duration.
Disadvantages
 Cannot study cause and effect relationships
 Cannot assess disease frequency
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CROSS-SECTIONAL STUDY
• It is also called epidemiologic study or prevalence study
• It analyses (describes)data collected on a group of
subjects at one point in time rather than over a period
of time. i.e they survey exposure and disease at a
single point in time.
• Both exposure and outcome variables are been
evaluated at the same point in time(without any inbuilt
directionality)
• Most sophisticated descriptive study
• It answers the question “WHAT IS HAPPENING RIGHT
NOW?”
With
outcome
subjects
Without
outcome
o
onset
time
QUESTION: “WHAT IS HAPPENING?”
NO DIRECTION OF INQUIRY
end
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
Cross-sectional studies
Disadvantages
Weakest observational design,
(it measures prevalence, not incidence of
disease). Prevalent cases are survivors
The temporal sequence of exposure and effect
may be difficult or impossible to determine
Usually don’t know when disease occurred
Rare events a problem. Quickly emerging
diseases a problem
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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 of
health services)
CORRELATIONAL STUDY DESIGN
ADV
• Compares events among
nations
DISADV
• Doesn’t compare
individuals, so it might lead
to overgeneralization.
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)
CASE CONTROL OR CASE HISTORY
STUDY
• A group of affected people is compared to unaffected
people(the control)
• It’s a LONGITUDNAL STUDY (like cohort study) because it’s
a study over a period of time.
• Subjects are selected based on a particular outcome and a
study backwards in time to try to detect the causes or risk
factors that may have earlier been reported in a descriptive
study
• Subjects are then matched and assigned into the two
groups. Subject selected on the basis of disease[e.g lung
cancer].
• Sometimes called a retrospective study because of the
direction of study
CASE CONTROL OR CASE HISTORY
STUDY
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
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
COHORT STUDY
• A cohort is a grp of people who have something
in common and remain part of a group over an
extended time
• A group of people exposed to a suspected
etiological agent are compared with a matched
control 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
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
Disadv of cohort study
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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
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
UNCONTROLLED EXPERIMENTAL
STUDIES
• Intervention is not compared with a control
• The aim is to confirm that the Intervention
made a difference
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
CONTROLLED EXPERIMENTAL STUDIES
• Blind trial-single or double
• Control could be:
A. METHODOLOGY
1. Concurrent or parallel: randomized or nonrandomized(quasi)
2. Sequential control: self controlled or cross
over
3. External control
B. STUDY POPULATION
1. Clinical trials
2. Field trials
3. Community trials
EXPERIMENTAL STUDIES
ADV
• Best study type
• Greatest proove of causality
• Gold standard for other
design
• Least bias
• Proves best tx or procedure
efficacy
DISADV
• Greatest expense
• Long duration
• Unproven facts adopted by
community can hinder
study acceptance
overview
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 a
healthier us.
THANK YOU
FOR
LISTENING.