who/emro rpc unit · 3/26/2014 · *to test the hypothesis : confirm or reject it (etiology) - to...

Research Methodology Workshop

Research design/Strategy

Prepared by

Dr.Mahmoud Attia Abd El Aty Research Advisor

Directorate of Research and Studies

DG of Planning – MoH (HQ), Oman

24-26 March, 2014, Muscat

Dr.Mahmoud Attia Abd El Aty

Research design/Strategy “Study

Types” : Contents:

-General steps of research

- Different epidemiological study designs

- Descriptive vs. analytic study designs.

- Flow charts of analytic study designs

- Measurements of association

- Steps in analytical studies

- Comparison of the analytic Study designs to choose the appropriate design


Study Type(Design)

DescriptiveE.g. Cross-section

Analytical(Comparison)

Observational Experimental

Cohort Study

Case-control

Cross-section

Exposure Outcome

Exposure & Outcome at the same time

Exposure Outcome

Prof. Mahmoud Attia Abdelaty, Research AdvisorDr.Mahmoud Attia Abd El Aty

Cross sectional: “Snap-shot studies” (Exposure & Outcome are measured concurrently at the same

time - e.g. water supply and diarrhea among children

Time

Prospective/ Cohort Retrospective

Longitudinal Dr Mahmoud Attia Abdelaty, Research Advisor

Time span

studies

Direction of Exposure and Outcome


Types of Research Design

:I- Descriptive/ Non formal comparison studies When we need more/detailed information about risk factors or disease.

- Case report /series: Describe in depth the characteristics of one or a limited number of unusual cases

- Cross-sectional surveys : quantify the certain variables in a study population

- Ecological /correlation studies (Population/groups are the unit of study

rather than the individuals

- Surveillance:

II- Analytical/ etiological / Formal comparison studies: These studies are used to identify the determinants of diseases

A-Observational studies - Case-control studies - Cohort studies (Prospective – Retrospective) - Cross-sectional comparative studies B-Experimental Studies: The researchers control the exposures e.g Treatment

-Clinical trials: -Randomized Controlled Trials - Quasi-experiment

-Community Trials: -Vaccination - HE for cancer screening -Sanitation, -lifestyle intervention and CND -Elderly home care


Major differences between analytic (comparison) and

descriptive research designs

Descriptive Studies

Selection of Comparison group:

*No formal/ typical comparison -May divide participants into subgroups for

internal comparison Uses: -When relatively little is known about the risk

factor or disease/phenomena eg. AIDs -Description of occurrence, distribution of the

phenomena in relation to: Person, place, time and family formation var.

- Trend analysis over time: lifestyles, mortalities -Generate/suggest hypothesis -They are observed rather than tested (no Prior hypothesis)

Measure the effect or association: Not try to quantify the relationship

Analytical Studies Selection of Comparison group: *Formal comparison groups:

Exposure Status.: Cohort Disease/outcome: case-control

Uses: *To test the hypothesis : Confirm or reject it (etiology) - To identify the determinants of diseases (Prior hypothesis) Measure the effect /quantify the

Strength of association: -Relative risk (RR) or risk ratio in cohort:

e,g 0.2 or 1 or 5

-Odds ratio “OR” (Estimated RR) in case control


Hierarchy of evidence for Strength of association

Randomized Controlled Experimental trials (the strongest evidence)

Cohort studies

Case Control Studies

Cross sectional studies ( the least evidence (


Flow chart of cohort study design and measurement

Un-exposed

(Control) Exposed

Smoking

1000

No Smoking

1000

:Compare incidence rates

*Relative risk or risk ratio

Attributable risk*

Outcome

No CHD

Outcome

No CHD

Outcome

CHD 50

Outcome

CHD 20

Sample

Reference Population (Adult ≥ 40y)

Free from the outcome (CHD)

Incidence Incidence


Case-Control study design and measurement

Outcome absent

(Control)

200 without CHD

Outcome Cases (CHD):

200

Odds Ratio

)Estimated RR( a/b /cd=

ad/bc Ratio

Non-smokers

(b)

Non-Smokers

150 (d)

Smokers 150 (a)

Smokers

50 (c)

Usually Selected

separately

(Adult ≥ 40y)


Cross Sectional study design and measurement

Un-exposed Exposed

Smoking

1000

No Smoking

1000

At the same time - “Compare prevalence rates”

Outcome

No COPD

Outcome

No COPD

Outcome

COPD 50

Outcome

COPD15

Sample

Reference Population (Adult ≥ 40y)

Prevalence Prevalence


Measurements of association

*Incidence rate: *Relative risk (Risk Ratio): Incidence of disease among exposed group/ Incidence of disease among Un-exposed group =0.2 or 1 or 6 times *Attributable risk: Difference between the two incidence rates

* Odds Ratio: Estimated Relative risk in Case Control study. Ratio of odds of exp. among diseased (a/d) to the odds of exp. among non-diseased (c/d) cross product ad/bc

* Prevalence rate (in cross-sectional studies)= Total existing cases (Old and New) during a specified

period × Constant /Total Population during that Period (Usually at mid-period )


Steps in Analytical Studies :

Analytic studies are used to identify the determinants of diseases, or reasons for relatively high or low frequency in specified group.

-Define the hypothesis to be tested.

-Definition of the exposure (smoking) and outcome under study (CHD, COPD, Cancer)

Vaccine e.g HBV or Measles and antibodies or

disease (outcome).

-Select the most appropriate study design to test the study hypothesis.


The selection of an appropriate research design depends on:

1. The state of knowledge about the problem

2. The nature of the problem/research question/hypothesis

3. The resources available for the research

4. The ingenuity and creativity of the researchers


Exercises

- Select the appropriate study type

Select the appropriate study type

Is BCG vaccination protective against Leprosy?

Association of smoking and lung cancer

Is there a risk of water sources and the diarrhoea among children <5 years old in a village.


Comparison of the Three Analytic Study designs

Cohort Case-

Control

Cross-Section

Starting

point/Disease

or Exposure

[Exposed and non]

Cases/disease

and control

Combination:

Free from both,

Have both,…,…

Sample

represents

Non-Diseased

[Population free from

the disease]-large

Uncertain Survivors at point

or period in time

rare disease _ Best _

Prevalent dise. Best

Planning/ adm + _ Best Dr.Mahmoud Attia Abd El Aty

Comparison of the Three Analytic Study Designs (Cont.)

Cohort Case- Control Cross-Section

Outcome

Comparison

Incidence of

disease in exposed

and unexposed

Odds of exposure

in cases and

controls

Prevalence of

disease in exposed

and unexposed

Risk (measure of

effect)

RR– AR based on

incidence (Precise)

Odds ratio

(estimated RR)

Prevalence ratio

Temporality Certainly Not certain Not certain

Attrition +++ problematic ? No ++ Possible

Selective recall --- +++ problematic ++ Possible

Selective survivals + +++ problematic +++ problematic

Time/sample size/ cost

++++ +

++


who/emro rpc unit · 3/26/2014 · *to test the hypothesis : confirm or reject it (etiology) - to...

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