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Pharmacoepidemiology:Pharmacoepidemiology:Application IApplication I
Teerapon Dhippayom
PharmD, MClinPharm, PhD
Basic Pharmacoepidemiology: Semester 2/2554
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Application of pharmacoepidemiology
Validity of research finding
Scope
Bias and confounding
Issues to be considered in
pharmacoepidemiological study
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Application of Pharmacoepidemiology
To promote the rational use of medicine
To investigate the safety of medicine
To investigate the effectiveness of
medicine
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Validity of research finding
Internal validity
The study measured what it set out to
External validity
The ability to generalize from the studyto the readers patient
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Validity of research finding
Internal validity
Systematic error Random error
Bias Confounding
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Bias
Bias in research process
Literature review and variable selection
Sample selection
Intervention or treatment
Exposure and outcome measurement
Data analysis Results interpretation
Paper publication
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Bias
Selection bias
The relation between exposure and outcome
is different for those who participate and
Information bias
A distortion in measuring exposure oroutcome data that results in different quality
or frequency of information between
comparison groups
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Bias
Bias
Selection bias
Sampling bias
Attrition biasRecall bias
Measurement bias
Response bias
Information bias
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Confounding
Confounding
A situation in which a measure of the effect
of the exposure with other factor(s) that
influence the outcome under study
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Confounding
GI bleedingAspirin
NSAIDs
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Confounding control
Confounding control
Study design
Restriction
Matching
Data analysis
Stratification
Multivariate
analysis
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Issues to be considered
What to look for in observational studies
Is selection bias present?
Is information bias present?
Is confounding present?
If none of the above is presented, could
they be the results of chance
If all errors are excluded, the results might
be real and worthy of note
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Issues to be considered
Cohort study
Bias and confounding
Measurement and outcome
Follow-up time period
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Issues to be considered
Case-control study
Selection bias
Control selection
Sources of control group
Measurement and outcome
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Issues to be considered
Case selection
Well defined (inclusion criteria)
Represent population at risk
Incident case
Control selection
Risk of developing outcome case
Chance of exposing to risk factor case
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Issues to be considered
Sources of control group
Reduce referral bias
Community based
High cost and low compliance
Ideal, generalization
Hospital based
Convenience and low cost
May not represent the population at risk
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Issues to be considered
Measurement and outcome
Recall bias
Case and control group must be assessed
for exposure in the same way
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Application: an example
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Abstract
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Background
Several studies suggested the beneficialeffects of selected CHF drugs
in HF trials
Older patients may not received appropriate
HF drugs like younger patients
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Objectives
Compare outpatient CHF drug utilisationand hospital re-admission patterns in
patients 75+yrs with those age
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Methods
Nested case-control
Design
A French teaching hospital
Setting
12-month period (in 2000)
Study period
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Methods
All adults admitted to eight departments
Di n HF i h r
Study population
Standardised form? Claims for reimbursement under French
health insurance system
Data sources
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Methods
CHF drug utilisation patterns
Medication prescribed at discharged
Outcome measured
Medication prescribed during follow-up
Hospital re-admission patterns
Re-admission rate
Number of re-admission
Cumulative duration of hospitalisation
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Results
Patientcharacteristics
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Results
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Exercise
Odds ratio: calculation
Cases Noncases
OR =AD
BC
Exposed A B
Not exposed C D
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Disease conditions
Sample
Exposure torisk factor
Yes
Exercise
Population
at risk
w
disease(cases)
Samplewithout
disease
(controls)
No
Yes
No
Time
Research
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What is case
HF patients age 75+ years
Exercise
What is control
HF patients age 75 years or younger
What is exposing factors
HF medications
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Exercise
Calculate OR for prescribing of ACE inhibitors
> 75 years < 75 years
OR = = 0.5148 x 68
63 x 102
ACE inhibitors 48 63
No ACE inhibitors 102 68
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Results
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Results
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Internal validity
The study implication
Systematic error Random error
Bias Confounding
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Issues considered
Study design: Nested case control
Begin with a record of factors interested
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Identify case and control from a cohort
Look back for the expose of risk factors in
each group
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Issues considered
Selection bias
A French teaching hospital
L rin ll w-
Only 50% have their EF measured
Any different among group?
Number and type of concomitantmedication
Appropriate dose among group were not
measured
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Issues considered
Information bias
Appropriateness of diagnosis
Data from 8 different departments
Criteria for discharge diagnosis wasunknown
The completeness of the information
recorded It is not cleared if the re-hospitalisation
was for HF related
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Issues considered
Confounding bias
Confounding variables were adjusted
h r n i l n n r w r n
addressed Post-MI
Stroke
Cardiac surgery
etc
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Issues considered
Other issues
Hospitalisation among younger
patients appeared not different
The difference between two agegroup not prescribed HF drugs were
obvious, but yet not statistically sig.
Other factors may contribute to thelonger duration in older patient not
prescribed the drug
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Conclusion
The descriptive results on utilisationpattern in this study maybe useful
e mp ca on on ana y ca par s
questionable
It is crucial to evaluate the method
used before utilising the outcomes ofa study
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Questions