analytic studies

ANALYTIC STUDIES

Prepared By:Dr.Anees AlSaadiCMT-P R4December 2013

ANALYTIC STUDIES

• OUTLINE:–Hierarchy of Study design.– Introduction for analytic Studies./ Exposure &

Outcome. – Cohort and Case control Study design:• Definition. • Character.• Advantages and disadvantages.

ANALYTIC STUDIESIntroduction

ANALYTIC STUDIESIntroduction:

Testing specific hypotheses.

Samples of subjects are identified and information about exposure status and outcome is collected.

ANALYTIC STUDIESIntroduction:

Groups of subjects are compared in order to estimate the magnitude of association between exposures and

outcomes.

ANALYTIC STUDIESIntroduction:

The two main types:

Cohort study

Case-control study

ANALYTIC STUDIESIntroduction:

Exposure

Outcome

ANALYTIC STUDIESCohort study:

Exposure

Outcome

ANALYTIC STUDIESCohort study:

Definition

ANALYTIC STUDIESCohort study:

Definition

ANALYTIC STUDIESCohort study:

Definition

. Is an analytic epidemiologic research design in which the study population is composed of individuals who are classified as exposed and no exposed to particular risk factors. These groups are followed forward for a specific period of time to estimate the incidence rate of an outcome or the development of a health problem.

ANALYTIC STUDIESCohort study:

Exp

osed

Gro

up

Already exposed.

Casual factors

Protective factors

Non

Exp

osed

G

roup

Not exposed

Protective factors

Casual factors

Hypothesized to be at greater risk or lesser risk of developing the health problem

ANALYTIC STUDIESCohort study:

What is the Potential Source of Study Subjects…… ?

ANALYTIC STUDIESCohort study:

Study Subjects in Each Groups

followed in same manner.

Developing problem.

Death.

Study Ends.

Lost to follow up.

Not developing problem.

ANALYTIC STUDIESCohort study:

Cohort study

Prospective

Exposure status is determined when the

study begins.

Followed forward in time to observe the

outcome.

Historical

The exposure happened before the study begins.

ANALYTIC STUDIESCohort study:

Example

ANALYTIC STUDIESCohort study:

The most important bias is loss of follow ups (drop out).

ANALYTIC STUDIESCohort study:

Advantages:

• More control on data collection.

• Easy checking the study outcome.

• Clear temporal sequence. • Estimating the risk.• Good to study rare risk factors.• Can study different disease or

outcomes.

Disadvantages:

• Only risk factors defined at the beginning of the study can be studied.

• Costly.• Time consuming.• For common diseases.• The exposure status may

change during the study. • Loss of follow up.

ANALYTIC STUDIESCase Control Study:

Definition

It is analytic type of epidemiologic research design in which the study population consists of groups who either have

(cases) or do not have (controls) a particular health problem or outcome.

ANALYTIC STUDIESCase Control Study:

ANALYTIC STUDIESCase Control Study:

The investigator selects the case and the control group on the bases of the outcome and compares them in term of their

frequency of past exposure to the possible exposure.

ANALYTIC STUDIESCase Control Study:

Retrospective Study

ANALYTIC STUDIESCase Control Study:

Cases

Controls

ANALYTIC STUDIESCase Control Study:

Cases Study subjects who have outcome to be investigated.

Case definition: Objective description of the case.

Eligibility Criteria.

Controls Study subjects who do not have the outcome to be investigated.

Similar to the cases in most of the aspects except outcome.

Sources:

Hospital

Community

ANALYTIC STUDIESCase Control Study:

ANALYTIC STUDIESCase Control Study:

Controls

Cases

Similarity

ANALYTIC STUDIESCase Control Study:

• Selection of controls:–No outcome.–Selection randomly or Systematic.–Matching on specific variables./individual or

frequency.–Restriction.

ANALYTIC STUDIESCase Control Study:

What is the Potential Source of Study Subjects…… ?

ANALYTIC STUDIESCase Control Study:

The most important bias is recall .

ANALYTIC STUDIESCase Control Study:

Advantages:

• Quick design saves time.• Easy to perform.• Inexpensive. • Suitable for rare diseases.• Can study many risk factors.• Useful for generating

hypothesis.

Disadvantages

• Recall bias. • Can not be used for incidence rate. • Temporal relationship. • Can study only one disease

outcome. • Can only obtain relative measure

of risk.

Practical Exercise

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