making evidence more accessible using pictures rod jackson oxford 8/9/09
TRANSCRIPT
Making evidence more accessible using pictures
Rod Jackson
Oxford 8/9/09
What is Evidence Based Practice?
What is Evidence Based Practice?
The 6 steps of Evidence Based Practice
1. ASK a focussed question2. ACCESS - search for epidemiological evidence to
help answer question3. APPRAISE the evidence for its validity, effect size,
precision)4. AGGREGATE the evidence with patient/community,
clinical/hlth & policy issues & make an evidence-based decision
5. APPLY your decision6. [AUDIT your practice (i.e. check your actual practice
against evidence-based practice on a regular basis)].
The GATE frame
Graphic Approach To Epidemiology
©
Participants
Exposure Group Comparison Group
OutcomesTime
P
E C
O
T
PECOT: the 5 parts of every epidemiological study
All epidemiological studies can be hung on the GATE frame
EBP Step 1: ASK - turn your question into 5 parts (PECOT)
1. Participants (patient(s) you want to treat)
2. Exposure (an intervention if about therapy)
3. Comparison (there is always an alternative! - another therapy, nothing …
4. Outcome (usually a disease or condition you want to prevent or manage)
5. Time frame (over which you expect a result)
EBP Step 2: ACCESS - search for the best evidence to answer your questions
Use the PECOT components to choose search terms
P
E C
OT
• P
• E
• C
• O
• T
• Recruitment
• Allocation
• Maintenance
• Blind or
• Objective measurements &
processes
EBP Step 3: Appraise the evidenceusing PECOT & RAMBO on the GATE frame
EBP Step 4: AGGREGATE the relevant information & make an evidence-based decision:’ the X-factor
©
Epidemiologic evidence
Clinical / population
health considerations
Policy issues
Patient / community preferences
X-factor: making evidence-based decisions
expertise: ‘putting it all together’ the art of practice
Step 5
APPLY
Implementation!
Step 6: AUDIT - evaluate & improve performance
1. Determine ‘best’ practice (EBP Steps 1-4)
2. Assess current practice: survey
3. Compare with best practice - is there a gap?
4. Consider reasons for gap, identify processes to
reduce gap & implement
5. Re-survey: is there any improvement?
= quality improvement / audit
GATE Graphic Approach To Epidemiology
Graphic Appraisal Tool for Epidemiology
Graphic Architectural Tool for Epidemiology
www.epiq.co.nz
The GATE frame
©
the shape of every epidemiological study
GATE study design (PECOT)
P
E C
O
T
GATE study analyses (EGO & CGO)
a b
c d
EG CG
GATE study appraisal (RAMBO)P
E C
OT
Recruitment
Allocation
Maintenance
Blin
d or
Obj
ectiv
e m
easu
rem
ents
& p
roce
sses
GATE study design (PECOT)
Participants
Exposure Group Comparison Group
OutcomesTime
P
E C
O
T
Participants
Study Setting
Eligible Participants
ParticipantsP
Exposure & Comparison Groups
Exposure or Intervention Group
(EG)
Comparison or Control Group
(CG)EG CG
Outcomes (O)
Outcomes (O)Oa b
c d
yes
no
‘Dis-ease’
Time (T)
T
incidence
prevalence
GATE study analyses
Denominator (Participants)D
N Numerator (Outcomes)
O = N÷DO = N÷D
All epidemiological studies involve measuring the OCCURRENCE of disease
Occurrence = Numerator ÷ Denominator
GATE study analyses
P
EG CG
O
Denominator 1:Exposure Group
EG
Numerator 1:a
Denominator 2:Comparison Group
CG
Overall Denominator
a b
c d
Numerator 2:b
Occurrence = N ÷ D
P
EG CG
O
Denominator 1:Exposure Group
EG
Numerator 1:a
Denominator 2:Comparison Group
CG
a b
c d
Numerator 2:b
Exposure Group Occurrence:EGO = a ÷ EG
Comparison Group Occurrence:CGO = b ÷ CG
Estimating effects & associations involves comparing occurrences
Relative Effect or Risk = EGO ÷ CGO
e.g. relative risk (RR), risk ratio, prevalence ratio, incidence ratio
Absolute Effect or Risk Difference = EGO - CGO
e.g. risk difference (RD), absolute risk
Number Needed To Treat (NNT) = 1 ÷ RD
Analyses
it’s all about EGO & CGO
Occurrence = N÷D per unit of timeP
EG CG
O
Denominator 1:Exposure Group
EG x T
Numerator 1= a
Denominator 2:Comparison Group
CG x T
a b
c d
Numerator 2 = b
Exposure Group Occurrence:EGO = a ÷ (EG x T)
Comparison Group Occurrence:CGO = b ÷ (CG x T)
‘person-time exposure’
GATE study appraisal (RAMBO)P
E C
OT
Recruitment
Allocation
Maintenance
Blin
d or
Obj
ectiv
e m
easu
rem
ents
& p
roce
sses
Study appraisal
How well was the study done?
Was it ok ( or +) or not ok ()?
or unclear (?) or not applicable (n/a)
‘no study is perfect!’
RAMBO
E C
OT
appropriate Recruitment?participants representative
of target populationP
Study setting & eligibility criteria well described?
Recruit random sampleORRecruit consecutive eligibles
‘appropriateness’ depends on study question
RAMBO
EG CG
OT
appropriate Allocation process?were EG & CG comparable
P
Allocation process well described?
If allocated by investigators:Allocated randomly (e.g drugs)ANDConcealed allocationORIf allocated by measurement (e.g. smoking): Adjusted for differences between EG & CG (e.g. statistical or matching)
Allocate
EG CG
OT
P
RCT: Allocate randomly by investigators (e.g drugs)
EG CG
OT
P
Cohort: Allocate by measurement (e.g. smoking)
RAMBO
EG CG
OT
good Maintenance?did participants remain in
allocated groups (EG & CG)
P
Participants &/or investigators blind to exposure (and comparison exposure)?
Compliance high & similar in EG & CGContamination low & similar in EG & CGCo-interventions low & similar in EG & CG
Completeness of follow-up high & similar in EG & CG
RAMBO
EG CG
OT
Blind or Objective?measurements & processes
P
Allocation concealed (blind) if randomisedEG & CG measurements well describedOutcome measurements well described
Allocation/Measurement process similar for all participants
If measurement not objective (eg. automated or definitive) were assessors blind to exposure (and comparison exposure)
A
The GATE approach: every epidemiological study hangs on the GATE frame
There is only one basic study design:
• Cohort (& case-control) studies - aetiology / prognosis / intervention
• RCT (a randomised cohort study)- interventions
• Cross-sectional studies - diagnosis
Cohort (follow-up) study: archetypal epidemiological approach
Participants
Exposure Group Comparison Group
OutcomesTime
P
E C
OT
Allocated by measurement (not by randomisation)
Best design for investigating aetiology (risk), prognosis
Randomised controlled trial - cohort study where exposure allocated by randomisation process
Participants
Exposure Group Comparison Group
OutcomesTime
P
E C
OT
Allocated by randomisation
Best design for investigating treatments
Case series is a Cohort study with no comparison group
Participants
Exposure Group
OutcomesTime
P
E C
OT
Allocated by measurement
Before-after study
Participants
Exposure Group
Comparison Group
OutcomesTime
P
C
OT
Allocated by timing of intervention
E
Cross-over trial
Participants
Exposure Group 2
Comparison Group 2
OutcomesTime
P
C2
OT
Allocated by randomisation
E2
E1
C1
Exposure Group 1
Comparison Group 1
Cross-sectional study
Participants
Exposure Group Comparison Group
OutcomesTime
P
E C
OT
Allocated by measurement
real-life time
best design for prevalence and diagnostic test accuracy
Diagnostic test accuracy studyP
EG CG
O
Disease +ve
Test
Disease -ve
a bc d
Likelihood +ve test if D+ve:EGO = a ÷ EG
Likelihood +ve test if D -ve:CGO = a ÷ CG
+
-
Diagnostic test accuracy studyP
EG CG
O
Disease +ve
Test
Disease -ve
a b
c d
Likelihood -ve test if D+ve:EGO = c ÷ EG
Likelihood -ve test if D -ve:CGO = d ÷ CG
+
-
Diagnostic test for disease prediction
P
EG CG
O
Test +ve
Disease
Test -ve
a b
c d
Likelihood of D if test +ve:EGO = a ÷ EG
Likelihood of no D if test -ve CGO = d ÷ CG
+
-
Positive predictive value Negative predictive value
Diagnosis: test accuracy
EG CG
OT
est
a b
c d
+
-P
P
CG
EG
Disease + -
+
- + -
Diagnosis: test accuracy
EG CG
OT
est
a b
c d
+
-P
P
CG
EG
Disease + -
+
- + -
Diagnosis: disease prediction
Case control study
for investigating aetiology, interventions when outcomes rare
Exposed Not Exposed
Cases a bControls c d
Case control study
Exp. Not Exp.
Cases a bControls
Participants
Exp Group Comparison Group
OutcomesTime
P
EG CG
OT
cases
‘nested in a virtual cohort study’
a b
controls
eg cg
P
ComparisonE1
CE2E3Multiple Exposure
categories
Multiple Outcome categories
GATE: multiple categories
Participants
P
Continuous measure of Outcomes e.g. lipids
Olow
medium
high
high..med..low
Continuous measure of Exposure: e.g. body mass index
E
Correlation coefficient
GATE: continuous measurements
Participants
Life is a non-randomised trial
The 6 steps of EBP
1. ASK a focussed question2. ACCESS - search for epidemiological evidence to
help answer question3. APPRAISE the evidence for its validity, effect size,
precision)4. AGGREGATE the evidence with patient/community,
clinical/hlth & policy issues & make an evidence-based decision
5. APPLY your decision6. AUDIT your practice (i.e. check your actual practice
against evidence-based practice).
A CAT documents the steps for a specific question
CATS
Download from www.epiq.co.nz
GATE-lite