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8/12/2019 Penelitian Kilinis (Etiologi)
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CLINICAL RESEARCHETIOLOGYProf.Dr.dr . Rusdi Lamsudin, M .Med.SC, SpS(K)
Clinical Epidemiology & Biostatistics Unit/
Department of Neurology
Fakulty of Medicine
Gadjah Mada university
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Inference cause effectrelationship
Coffee drinking & MI
Hypertension & Stroke Smoking cigarettee & Stroke
Eating satae kambing & Hypertension
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Coffee drinking & MI
Explanation Type of assoc Basic for assoc Whats really
going on in the
population
1. Chance Spurious Random error Not related
2. Bias Spurious Systmatic error Not related
3. Effect-cause Real Cart before the horse MI is a cause of Coffee
drinking
4. Effect-effect Real Counfounding Coffee dringking & MI
caused by a third,extrinsic factor
5. Cause-effect Real Cause and effect Coffee drinking is a
cause of MI
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Designing for Etiologic Study
Experiments
Cohort
Cross-sectional
Case-control
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Cohort StudyPrimary purposes
Descriptive - Incidence Analytic - analyze associations between
risk factors and those outcomes
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Cohort Studies
Prospective cohort studies
Retrospective cohort studies
Nested case-control studies Double-cohort studies and external
controls
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Prospective cohort design
Risk factor
presentRisk factor
absent
Disease No disease
Disease No disease
Population
Sample
THE PRESENT THE FUTURE
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Porspective Cohort Design
Strengths
Powerful strategy for defining the
incidence and investigating the potential
causes of a condition
The time sequence strengthens the
inference that factor may be a cause of theoutcome
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Porspective Cohort Design
Strengths (Cont)
Gives the investigator an opportunity to
measure important variables completelyand accurately
Especially valuable for studying theantecedents of fatal diseases
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Porspective Cohort Design
Weaknesses
Expensive
ineffeicient Cannot be used for studying rare diseases
Need large number of subjects for long
periods of time
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Retrospective cohort design
Risk factor
presentRisk factor
absent
Disease No disease
Disease No disease
Population
Sample
THE PAST THE PRESENT
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Retrospective cohort designStrengths
Can establish that predictors variables
preceded the uotcomes
Guarantee that measurement of predictors
variables was not biased
much less costly and time-consuming thatprospectives ones
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Retrospective cohort designStrengths(Cont)
The subjects are already assembled,
baseline measurements have already been
made and the follow-up period has already
taken place.
All subjects who developed the outcome of
the subjects who developed the outcome
(cases) and all those did not (controls)
come from the same population
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Retrospective cohort designWeaknesses
Investigator has no control over the nature
and the quality of the measurements that
were made
The existing data may not include
information that is important to answeringthe research question
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Nested case-control design
Disease present
Disease absent
Risk factor
present
Risk factor
absent
Risk factor
present
Risk factor
absent
THE PRESENT
MEASUREMENT IN
PRESENT; SPECIMENT
FROM THE PAST
Study cohort
Population
All
cases
Sample
of
control
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Prospective double-cohort design
Risk factor
present
Risk factorabsent Disease No disease
Disease No disease
THE PRESENT THE FUTURE
Pop #1
Pop #2
Sample (cohort #1
Sample cohort #2
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STEPS IN PLANNING
A COHORT STUDY When to use a cohort design
Choosing among cohort designs
Selecting subjects Measuring predictor and confounding
variables
Following subjects and measuringoutcomes
Analysing incidence and RR
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Cross-sectional design
Risk factor;
Disease
Risk factor;
No disease
No risk factor;
Disese
No risk factor;
NO disease
THE PRESENT
Population
Sample
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Cross-sectional design
(Strengths)
No waiting to see who will get the disease
fast and inexpensive
no problem with loss of follow-up
the only one to give the prevalence of
disease or risk factor
convenient for examining networks of
causal links
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Cross-sectional design
(Weaknesses)
Difficult to establish causal relationship
Impractical for the study if the design
involving collecting data on a sample of
individuals from the general population
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Case-control design
Disease
Risk factor
absent
Risk factor
present
Risk factor
absent
Risk factor
presentNo disease
THE PAST OR PRESENT
THE PRESENT
Sample
of cases
Sample
of
control
Pop
withdisease
(cases)
Pop
without
disease
(control
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Case-control design
(strengths) Well suited to study of rare diseases or these with long
latency
Relative quiks to mount and conduct
Relative inexpensive
Requires comparatively few subjects
Existing records can occasionally be used
No risk to subjects Allows study of multiple potential causes of disease
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Case-control design
(weaknesses) Relies on recall or records for information on past
exposure
Validation of information is difficult or sometimes
impossible
Control extranous variables may be incompleted
Selection of appropriate comparison group my be difficult
Rates of disesase in exposed and unexposed individuals
cannot be determined
Methods relatively unfamiliar to medical community and
difficult to explain
Detailed study of mechanism is rarely possible
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Step-by-step of planning and
conducting of case-control study Developing and stating the background of the study
Stating the research question
Stating the hypotheses
Clearly defining the disease under study and exposure of
interest
Selecting the cases
Defining and selecting a control group developing and testing research instruments
Conducting field operations
Planning the statistical analysis