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8/2/2019 A4 Cross Section
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Cross-sectional Study designs
Dr Hamid Hussain
8/2/2019 A4 Cross Section
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LEARNING OBJECTIVES
Learner should be able to know at the end of this lecture
Classify study designs?
Descriptive and Analytical epidemiology?
What is a cross-sectional study?
When to conduct cross-sectional study?
How to test the hypothesis by means of a cross-
sectional study?
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PERFORMANCE OBJECTIVES
LEARNER SHOULD BE ABLE TO
Conduct the cross-sectional study for
any new hypothesis
Apply this cross sectional analytical
method when situation demands
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Study design: Definition
A study design is a specific plan
or protocol for conducting thestudy, which allows the
investigator to translate the
conceptual hypothesis into an
operational one.
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Study designs
Study types
Descriptive(formulationhypothesis)
Individualbased
Case studies
Case series
Populationbased
co-relational
Analytical(testing
hypothesis)
Observational
Case-control
cohort
Cross-sectional
Interventional
RCTs (III)
Quazi experimental
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Descriptive Studies
Descriptive studies describe the pattern ofdisease in relation to Person, Place andTime.
Descriptive studies use information from
diverse sources like clinical records ofhospital or private practices as well asnational figures.
While features inherent in their design
preclude the ability to test hypotheses,these studies are very useful to describethe pattern of disease occurrence as wellas formulate research questions.
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Descriptive Studies
Descriptive studies are the mostfrequently encountered study
design
The identification of descriptive
characteristics frequently constitutes
an important first step in the searchfor determinants or risk factors that
can be altered or eliminated to
reduce or prevent the disease.
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Case Report
Case Series
DescriptiveEpidemiology Study
One case of unusual
finding
Multiple cases offinding
Population-basedcases with denominator
Descriptive study designs
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Descriptive Studies
Case-control Studies
Cohort Studies
Develop
hypothesis
Investigate its
relationship to
outcomes
Define its meaningwith exposures
Clinical trialsTest link
ex erimentall
IncreasingKnowledgeof
Disease/Exp
osure
Cross sectional studies
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Study Designs -
Analytic Epidemiology
Experimental Studies Randomized controlled clinical trials
Quazi experimental studies
Observational Studies Group data
Ecologic
Individual data
Cross-sectional
Cohort
Case-control
Case-crossover
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Cross-sectional study
A cross-section is the shape that results fromcutting a slice from an object.
The sampling frame usually conforms to the
snapshot analogy.
A cross-sectional study studies, disease and risk
factor patterns in a representative part of the
population, in a narrowly defined time period.
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Cross Sectional
12
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Cross sectional study
Primarily, this study provides information
on prevalence of disease and risk factors.
The measurements are made over a
relatively short period of time such as a year
or two.
Excellent for measuring the population
burden of disease.
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Cross-sectional study
It also can seek associations, generate and
test hypotheses and, by repetition, be used
to measure change.
Ideal cross-sectional study is of a
geographically defined, representativesample of the population studied within a
slice of time and space.
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Cross sectional study
People representing virtually all stages
of health and disease.
Indirect insights on the natural history.
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Cross-sectional studies
An observational design that surveys
exposures and disease status at a single point
in time (a cross-section of the population)
time
Study only exists at this point in time
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Cross-sectional Design
time
Study only exists at this point in time
Study
population
No Disease
Disease
factor present
factor absent
factor present
factor absent
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Design
Define population
Gather Data on Exposure and Disease
Exposedand have
the disease
(a)
Exposedbut have
no disease
(b)
Not
Exposed
and have
the disease
(c)
NeitherExposed
nor have
the disease
d
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Analysis: Cross Sectional design
Disease No disease
Exposed a b
Not exposed c d
Total a + c b + d a+b+c+d
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Odds Ratio
Number developing DVT among OC users/ Number developing DVT among Nonusers
NOT developing DVT among OC users/ NOT developing DVT among Nonusers
Odds Ratio = 40/10 20/30 = 4/0.67 = 5.97 or 6
The odds of DVT in OC users was
6 times the odds of DVT in NON OC users
Disease DVT No DVT
Used OC 40 20
No OC 10 30Exposure
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Cross-sectional Studies are Often used
to study conditions that are relatively frequent
with long duration of expression (nonfatal,
chronic conditions) It measures prevalence
It can not measure incidence of disease
Not suitable for studying rare or highly fatal
diseases or a disease with short duration
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Cross-sectional Studies
Advantages;
Easy to carry out.
Economical to conduct
Rapid method for collecting health information
as part of Rapid Epidemiological Assessment
(R.E.A) methodology. Can be conducted to assess the health care
needs of the population.
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Advantages;(contd)
Helpful in measuring access and utilization of
health services.
Helpful in developing an etiological hypothesis.
Provides information between disease and various
variables.
Provides information regarding distribution of a
disease. Determines burden of the diseases in a population.
So helpful for planning purposes.
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Cross-sectional studies Disadvantages
Weakest observational design, (it measures
prevalence, not incidence of disease). Gives no measure
of new cases occurrence
The temporal sequence of exposure and effect maybe difficult or impossible to determine So gives noinformation whether which comes first e.i. Cause or Disease.
Rare events are a problem.
Prevalent cases are survivors. Gives no direct idea aboutnatural history of the disease or etiology.
Neymans bias. Miss earlier cases that have died or recovered