A4 Cross Section

8/2/2019 A4 Cross Section

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Cross-sectional Study designs

Dr Hamid Hussain


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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

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