study design in research

STUDY DESIGN IN

RESEARCH

Dr. Kusum GaurProfessor, PSMWHO Fellow IEC

* Few jewels from ocean

Dr. Kusum Gaur 2

Definition of Research

“Research is a

systematized effort

to gain new knowledge”.

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1. Collect review of literature/Situation Analysis2. Identify and prioritize health problems3. Decide aims & objectives4. Planning Methodology including study design5. Execution6. Compilation, Classification & Presentation of data7. Analysis8. Test of Significance/Test of Hypothesis9. Inferences10. Report Writing11. Dissemination of Report

Steps in Research (Holy 11)

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Study Design

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.

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Retrospective

Prospective

Cross -sectional

4. Ambidirectional

Direction of Study

Backward Forward

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Decision Tree

Observational Study

Intervention Done

No Yes

Experimental Study

Comparison Group

Descriptive Study Analytic Study

Cohort StudyCross-Sectional Study

Case-Control Study

Randomization

NRCT Study RCT Study

Direction of Study

E O

NoNo

YesYes

E OE = O

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Epidemiological Study DesignObservational Studies Descriptive Studies

AnalyticCross-SectionalCase-ControlCohort

Experimental / Interventional studiesAs per Control: RCT/NRCTAs per Blinding: Single /Double Blind As per Design: Simple/Cross-overAs per Area: Field/Clinical/Lab


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Descriptive Studies

• Case reports

• Case series

• Population studies


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Descriptive Studies: Uses

• Hypothesis generating

• Suggesting associations

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Descriptive Type of Observational Study

• Other Name Case-Series/Population• Unit of Study Case/Individuals• Study Question What is happening • Direction Of Inquiry• Study Design

☻☻☻☻☻☻ desired information

☻☻☻☻☻☻ about cases/individuals is collected


Case-Series …….

Advantages• Easy to do• Excellent at identifying unusual situation• Good for generating hypotheses

Disadvantages• Generally short-term• Investigators self-select (bias!)• no controls 09/03/2010 11Dr. Kusum Gaur

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Analytical Observational Studies

• Cross-sectional

• Case-control

• Cohort


Cross-sectional Study

• Data collected at a single point in time

• Describes associations

• Prevalence

A “Snapshot”


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Cross-Sectional Study

• Other Name Prevalence Study• Unit of Study Individual• Study Question What is happening • Direction of Inquiry• Study Design

Population

Diseased

Not Exposed to Factor

Exposed to Factor

Non-Disease

Exposed to Factor

Not Exposed to Factor 12/08/2012

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Objectives of a Cross-Sectional Study

To find out association

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Sample of Population

Regular Meditation

Not doing meditation

Prevalence of DM

Prevalence of DM

Time Frame = Present1612/08/2012 Dr. Kusum Gaur

Defined Population


DM+ -

Med

itatio

n +

- 220

2 98

680


E.G. Out of 1000 population if 100 were doing meditation regularly & out of that only 2 were having DM. Remaining 900 were not doing meditation at all, out of that 220 were having DM.

Cross-Sectional Study

• Strengths– Quick– Cheap

• Weaknesses– Cannot establish cause-effect

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Case-Control Studies

Start with people who have disease(Cases)

Match them with controls that do not have

disease (Match Confounding)

Look back and assess exposures

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Controls

A control is a standard of comparison (confounded with variability but without effect)

for

• Effects

• Variability

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Case-Control Study

• Other Name Retrospective Study • Unit of Study Cases/Control• Study Question What has happened • Direction of Inquiry= F O• Study Design

CasesNot

Exposed

Exposed

Control

Exposed

Not Exposed

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Objective of a Case-Control Study


To assess Risk Ratio

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Case-Control Study

Patients with DM

Persons w/o DM

PresentPast

Regular Meditation

Regular Meditation

No Meditation

No Meditation

Cases

Controls


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The logic of Case-Control Studies

Cases differ from controls only in having thedisease

If exposure does not predispose to having the disease, then exposure should be equallydistributed between the cases and controls.

The extent of greater previous exposure among the cases reflects the increased risk that exposure confers

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Case-Control Studies: Strengths

• Good for rare outcomes: cancer• Can examine relation of exposures to disease• Useful to generate hypothesis• Fast• Cheap• Provides Odds Ratio


Case-Control Studies: Weaknesses

• Cannot measure– Incidence– Prevalence– Relative Risk

• Can only study one outcome• High susceptibility to bias


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Cohort Study

• Begin with disease-free individuals

• Classify patients as exposed/unexposed

• Record outcomes in both groups

• Compare outcomes using relative risk

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Cohort Study• Other Name Prospective Study / Follow-up Study/Incidence Study

• Unit of Study Individual• Study Question What is happening • Direction of Inquiry F O• Study Design•

CohortCohort

Exposed to Factor

Not Non Diseased

Not Exposed to

Factor

Diseased

Diseased

Non-Diseased

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Logic of Cohort Study

Cohort is a group of persons sharing a common characteristics

Differences in the rate at which exposed andcontrol subjects contract a disease is due tothe differences in exposure, since others are known and similar.

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Cohort Study

Prospective (usually)

Controlled

Can determine causes and incidence ofdiseases as well as identify risk factors

Generally expensive, time consuming and difficult to carry out

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Steps for Cohort Study

Identify geographically defined groupIdentify exposed subjects and not exposed

subjectsFollow over a specific timeRecord the fraction in each group who

develop the condition of interestCompare these fractions using RR, AR or OR

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Objectives of a Cohort Study

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To assess Risk Ratio

To find out Relative Risk

To find out Attributed Risk

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Prospective Cohort Study

No Meditation

Regular Meditation

No DM

DM

DM

No DM

Present Future

Cohort

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Cohort Study: Strengths

• Can measure multiple outcomes

• Can adjust for confounding variables

• Can calculate Attributed Risk


Cohort Study: Weaknesses

• Expensive

• Time consuming

• Cannot study rare outcomes

• Confounding variables


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Measurements of Association

•Significance Test•Relative Risk•Attributable Risk•OR

•Significance Test•OR

Cohort Study Case Control Study

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Measures of Association

Significance Test – to test significance of difference in exposure between control and Cases

Odds ratio - ratio of the odds of contractingdisease in given exposure

Relative Risk – Ratio between incidence among exposed and incidence among non-exposed

Attributed Risk – percentage of difference between incidence among exposed and non-exposed with incidence among exposed

RR or OR of 1 indicate no effect of exposure (equal odds)

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Cases control

Exposed a b

Non-exposed

c d a x 1oo

Exposure Rates = in Cases (P2) a+c

b x 1ooExposure Rates = in Controls (P1) b+d

P2 – P1

Z Score = SEDP

P1Q 1 P 2 Q 2

SEDP = ------------- + -------- N 1 N 2

‘Z’ Score of Exposure Rates


ad ODD’s Ratio = Times

bc

Incidence among ExposedRR = Times

Incidence among Non-Exposed

a/a+b a (c+d)= = c/c+d c (a+b)


Attributed Risk

(Incidence among Exposed - Incidence among Non-Exposed)

AR = x 100 Incidence among Exposed

aIncidence among Exposed= x 100

a+b c

Incidence among Non-Exposed= x 100 c+d


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Experimental Studies

Clinical trials provide the “gold standard” of

determining the relationship between

factor and the event

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Types of Experimental Study

As per Randomization:

• Randomized Control Trials (RCT)

• Concurrent Parallel Design (RCT)

• Sequential RCT Design

• RCT with External Control

• Non – Randomized Trials

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Types of Experimental Study…. As per Construction:

• Simple

• Cross-Over Study Design

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As per Study Area:

• Field Trials

• Clinical Trials

• Lab. Trials

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Quality of Experimental Study

• Randomization

• Blinding

• Control

• Cross-Over

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Controls in Clinical Trials

A clinical trial is a comparative, prospectiveexperiment conducted in human subjects

• Historical controls are better than no controls

• Patients can serve as own controls - This is usually beneficial as the comparison removes patient differences

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Blinding

Good practice: factors that can affect the evaluation of outcome should not be permitted to influence the evaluation process

Single-blindPatient or evaluator (either of one) is blinded as to intervention

Double-blind designNeither patient nor outcome evaluator knows Rx to which patient was assigned

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Randomized Control Trials (RCT)

• Before and After Comparison

• Comparison with Placebo

• Comparison Of two medicine/procedure/tests

• Comparison Of > two medicine/procedure/tests

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Experimental Study

• Other Name Intervention Study• Objective To know the effect of intervention• Unit of Study Individual meeting entry criteria• Study Question What is happening after intervention in both

groups • Direction of Inquiry I E

• Study Design 1(Intervention with Placebo)

Group 1/cases Intervention Negative

Outcome

Positive Outcome

Group 2/control Placebo

Positive Outcome

Negative Outcome

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Clinical Trial

Study Population

Treatment Group

Control Group

Outcomes

Outcomes

R a n d om i z e

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Intervention Study - Design 2(Comparison of Effect of Two Interventions)

Cases Meeting

Entry criteria

Group -2

Negative Outcome

Group - 1

Positive Outcome

Negative Outcome

Intervention -1 Intervention - 2Intervention

Positive Outcome

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Cross Over Design Cases

MeetingEntry criteria

Group-2

Negative Outcome

Group -1

Positive Outcome

Negative Outcome

Intervention - 1Intervention - 2

Group -2Group -1

Intervention -1Intervention -2

Positive OutcomePositive

Outcome

Positive Outcome

Negative Outcome

Negative Outcome

Crossover

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Other Types of Experimental Study

• Quincy Experimental Study

• Block Experimental Study

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Quincy Experimental Study

Cases MeetingEntry criteria Group -2

Negative Outcome

Group - 1

Positive Outcome

Negative Outcome

Intervention No InterventionIntervention

Positive Outcome

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Block Experimental Study

Cases MeetingEntry criteria

Group -2

Negative Outcome

Group - 1

Positive Outcome

Negative Outcome

Intervention -1

Intervention-2

Intervention

Positive Outcome

Group -3

Positive Outcome

Negative Outcome

Intervention-3Intervention

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Steps of Experimental StudyDrawing up a Protocol

Reference Population

Sample Population

Exclusions

Randomization

Experimental Group Control Group

Manipulation/Intervention

Follow - up

Assessment of Outcome12/08/2012

Strength

Ideal Study Design for established causality

WeeknessEthical Issues

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STUDY QUESTIONS AND APPROPRIATE DESIGNS

Type of Question Appropriate Study Design

Burden of illness Field Surveys

- Prevalence Cross Sectional Survey

- Incidence Longitudinal survey

Causation, Risk & Prognosis Case Control Study,

Cohort study, RCT

Treatment Efficacy Randomized Controlled study

Diagnostic Test Evaluation Randomized Controlled study

Cost Effectiveness Randomized Controlled study

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Hierarchy of Epidemiological Study Design

Generate Hypothesis

Establish Causality

Case Report

Case Series

Cross-Sectional

Case Control

Cohort

RCT

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study design in research

Health & Medicine