Transcript STUDY DESIGNS AND MEASUREMENT

Evidence-based medicine process
Yodying Punjasawadwong MD., M.Med.Sc, FRCAT
Department of Anesthesiology
Chiang Mai University
Faculty of Medicine , Chiang Mai University
17 November, 2011
Contents:
 Definition of evidence-based medicine
 Steps in evidence based practice
 Asking answerable clinical questions
 Matching research designs to clinical questions
 A clinical question map for searching ( example )
 Example
 Level of evidence and recommendation
Definition
“Evidence Based Medicine is the conscientious,
explicit and judicious use of current best evidence
in making decision about the care of individual
patients.
“ Evidence Based Practice of Medicine is the
integration of the best available research evidence
with clinical expertise, patient values, and
circumstance”
( Gordon Guyatt 1992 )
Four steps in evidence-based practice
1. Formulation a clear clinical question
2. Search the literature for relevant articles
3. Critically appraise the evidence for its
validity and usefuleness
4. Implement useful finding in clinical
practice
How to practice EBM (the 6
Assess
patient
Ask
clinical question
Acquire
the evidence(s)
Appraise
The evidence(s)
Apply
the best evidence
Assess
your performance
As)
• History, physical exam and investigation
• Clinical expertise
• Recognize the knowledge gaps
• Use the PICO structure to form a question
• Search recent literature
• Search EBM resources or societies guidelines
• Use provided worksheets
• Use available software (catnipper)
• Rank the level of evidences and apply the best
• Integrate this with patient values and clinical expertise
• In the frequency of performing the whole process
• In the efficiency of performing each step
Asking answerable clinical
questions:
Why structure questions ?
1. Ensures efficient search strategy
2. Requires you to consider the patient
populations .. From which evidence can be
generalized to your patient
3. Defines your options for intervention
(exposure/study factor) vs. comparator
4. Defines the important outcomes ( to you;
your patient; society)
5. Defines the most valid study design
What questions do we answer?
: Most urgent
: Most interesting
: Most feasible to answer
:Most likely to recur
: Most examinable
Two types of clinical questions
•
Background
•
Foreground
Two types of clinical questions
Elements
Background
---------------------2-part
Foreground
-----------------------4(or3) part,PICO
Focus
general
specific
Asked by
learners
clinicians/patients
Example
What is…
How dose..
Answer
What is wrong with me?
Why am I sick ?
What is going to happen?
How should I be treated ?
stable..from
up to date..from
text book
research data
Rx
Foreground Qs-Med Js.
“Dated” information
Dx
Px
Pathology
Background Q- textbooks
Physiology
Not “dated”
Anatomy
student
Experience
intern
resident
consultant
Anatomy of question
P
I
C
O
= Population
= Intervention
= Comparison
= Outcome
(Among)
(Does)
(vs.)
(Affect)
M = Method (optimal study design)
Clinical Issues and Questions in the
Practice of Medicine
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Cross-sectional
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Cross-sectional
Cohort
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Cross-sectional
Cohort
Cohort, Case-control
Cohort
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Cross-sectional
Cohort
Cohort, Case-control
Cohort
RCT
RCT
Matching the strongest design to
clinical questions
Diagnosis
Prevalence
Incidence
Risk
Prognosis
Treatment
Prevention
Cause
Cross-sectional
Cross-sectional
Cohort
Cohort, Case-control
Cohort
RCT
RCT
Cohort, Case-control
Trish’s scenario
Trish, a secretary, is planning a quick
trip to & from the U.K ( ‘ long haul’) to
visit her sick aunt
- Trish is aged 59 yrs, post-menopausal,
taking HRT & is overweight.
- She has read in newspaper:
compression stockings stop DVTs’
- Trish asks you; “ Should I wear
compression stockings on the plane ?
Framing the question
Population ‘ air travel/ traveler”
Intervention ‘ compression stockings’
Comparison ‘ not use compression
stockings”
Outcome ‘ deep vein thrombosis
Asking Question:
Among air travelers (P)
Do compression stockings (I)
Compared with not using (C)
Affect ( the rate of ) DVTs (O) ?
A clinical question ‘map’
Why ?
: Suggests best study design
: Assists plan search strategies
A clinical question ‘map’
Question
------------Diagnosis
Study type
-----------cross sectional, analytic
Data base
------------Medline
Etiology
cohort, case-control
Medline
risk. tw
Medline
Medline
Cochrane
Library
Exp cohort studies/
clinical trial.pt
Meta analysis.pt or
Prognosis
cohort
Intervention RCTs
Systematic review
Best one-line search term
-------------------------------sensitivity. tw
Question and search
Among air travelers (P)
Do compression stockings (I)
Affect ( the rate of ) DVTs (O) ?
Study type: RCTs
Searching - Medline
Med line : Search for RCT
“ PubMed”
Use searching terms based on PICO
(Other interfaces: apply ‘ limited’
Publication Type- RCT..if excessive)
Searching result
1.
Deep vein thrombosis and airtrvel-the deadly duo.
AORN J 2003 Feb; 77(2):346-54
2.
Air travel and venous thrombosis Tidsskr Nor Laegeforen. 2002
Jan:122(16):1579-81. Norwegian
2.
Thromboembolism in travelers Orv Hetil 2001 Nov 11; 142 (45): 246973. Review Hungarian
4.
Venous air thrombo-embolism from air travel the LONGFLIT study.
Angiology. 2001 June;52(6):369-74
5.
Frequency and prevention of symptomless deep-vein thrombosis in long
haul flight: a randomized trial. Lancet 2001 May 12; 357(9267):1485-
6.
Economy class syndrome Aviates Space Environ Med 1994 Oct; 65(10
part 1):957-60
Selecting articles
1.
Deep vein thrombosis and airtrvel-the deadly duo. AORN J 2003 Feb; 77(2):34654
2.
Air travel and venous thrombosis Tidsskr Nor Laegeforen. 2002 Jan:122(16):157981. Norwegian
2.
Thromboembolism in travelers Orv Hetil 2001 Nov 11; 142 (45): 2469-73. Review
Hungarian
4.
Venous air thrombo-embolism from air travel the LONGFLIT study. Angiology.
2001 June;52(6):369-74
5.
Frequency and prevention of symptomless deep-vein thrombosis in long
haul flight: a randomized trial. Lancet 2001 May 12; 357(9267):1485-9
6.
Economy class syndrome Aviates Space Environ Med 1994 Oct; 65(10 part 1):95760
Basic Steps for Acquiring the Evidence to Support a Clinical Decision
Clinical problem
Define important, searchable question
Design search strtegy
Select relevant studies
Critical appraisal
Poo
r
Select second most
likely resource
Design search strategy
Critical appraisal
Apply the evidence
Apply the evidence
Sackets DL et al. 1998
Categories of evidence I
 I : Experimental study design/randomized controlled
trial(RCT)
 II: Quasi experimental study design/ non-randomized
controlled study design
 III:Non-experimental study design such as cohort
studies, correlation studies and case-control studies
 IV: Evidence from expert committee reports or
opinions/and/or clinical experience of respect
authorities
( adaped from AHCPR 1992 )
Categories of evidence I
 Ia : evidence from systematic review/meta-analysis of RCT
 Ib: evidence from at least one RCT
 IIa: evidence from at least one controlled study without
randomization
 IIb:evidence from at least one other type of quasi-experimental
studies
 III:evidence from non-experimental studies, such as comparative
studies, correlation studies and case-control studies
 IV:evidence from expert committee reports or opinions/ and /or
clinical experience of respect authorities
Strength of recommendation
 A directly based on category I evidence
 B directly based on category II evidence or
extrapolated recommendation from category I evidence
 C directly based on category III evidence or
extrapolated recommendation from category I or II
evidence
 D directly basd on category IV evidence or
extrapolated recommendation from category I,II or III
evidence
Factors contributing to the process of deriving
recommendations
 The nature of evidence ( e.g. its susceptibility to
bias)
 The applicability of the evidence to the population
of interest(its generaliaability)
 Resource implications and their cost
 Knowledge of the health care system
 Beliefs and value of the panel