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GATE:
Graphic Appraisal Tool for Epidemiology
1991
-
2015
1 picture, 2 formulas & 3 acronyms
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GATE:
Graphic Appraisal Tool for Epidemiology
Graphic Architectural Tool for Epidemiology
Graphic Approach To Epidemiology
making epidemiology accessible
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4th year medical students 1991
Jerry Morris
numerator
epidemiology =
denominator
In: Uses of Epidemiology 1957
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presentation outline
GATE is a framework for:
1. study design
2. study analysis
3. study error
4. practicing EBM
1 picture, 2 formulas & 3 acronyms
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GATE: a framework for study design
1 picture
every epidemiological study can be hung on the GATE frame
1 picture, 2 formulas & 3 acronyms
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1 picture: GATE frame
cohort of British doctors
smoking status allocated by measurement (observation)
smokers
yes
lung cancer
events counted no
non-smokers
followed for 10
years
cohort / longitudinal / follow-up study
1 picture, 2 formulas & 3 acronyms
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1st acronym: PECOT
British doctors
P
Participants
randomly allocated to aspirin or placebo
Exposure E C Comparison
aspirin
placebo
Outcomes
yes
MI
no
O
T
Time
5 years
randomised controlled trial
1 picture, 2 formulas & 3 acronyms
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middle-aged Americans
P
body mass index measured
overweight
diabetes status
measured in all
participants
yes
no
E C
‘normal’ weight
O
T
cross-sectional (prevalence) study
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middle-aged American
women
P
receive mammogram screening test
mammogram positive
breast cancer
E
C
mammogram negative
yes
O
no
T
diagnostic test (prediction) study
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middle-aged American
women
P
Gold Standard
breast cancer
positive
mammogram
negative
test
E
C
O
no breast cancer
T
diagnostic (test accuracy) study
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P
smokers
lung cancer
E
C
non-smokers
smoking status measured
cases
yes
O
no
controls T
case-control study
(all nested in virtual cohort studies)
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£100
GATE: a framework for study analysis:
1st formula: occurrence = outcomes ÷ population
the numbers in epidemiological studies can be hung on the
GATE frame
1 picture, 2 formulas & 3 acronyms
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1st formula: occurrence of outcomes =
number of outcomes ÷ number in population/group
British doctors
P
Participant Population
smoking status measured
Exposure Group EG CG Comparison Group
smokers
Outcomes
Lung cancer
non-smokers
yes
no
a
O
b
T
Time
10 years
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Population
P
British doctors
smoking status measured
Exposure Group EG CG Comparison Group
smokers
Outcomes
Lung cancer
non-smokers
yes
no
a
O
b
T
Time
10 years
Exposure Group Occurrence (EGO) = a÷EG
= number of outcomes (a) ÷ number in exposed population (EG)
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P
British doctors
Population
randomly allocated
Exposure Group EG CG Comparison Group
aspirin
Outcomes
MI
placebo
yes
no
a
O
b
T
Time
5 years
Comparison Group Occurrence (CGO) = b÷CG
= number of outcomes (b) ÷ number in comparison population (CG)
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Epidemiology = Numerator ÷ Denominator
middle-aged American
women
P
Participant Population
receive mammogram screening test
D
Exposure Group EG
mammogram positive
Outcomes
yes
breast cancer
no
a
Comparison Group
mammogram negative
N
T
Time
O
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the goal of all epidemiological studies is to
calculate EGO and CGO
P
British doctors
smoking status measured
smokers
yes
EGO:
Occurrence (risk) of
no
cancer in smokers
EG
a
CG non-smokers
O
b
Lung cancer
10 years
T
CGO:
Occurrence of
cancer in nonsmokers
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P
Middle-aged Americans
Body Mass Index (BMI) measured
High BMI
EG CG
Low BMI
high
low
EGO:
Average blood
glucose in EG
O
CGO:
Average blood
glucose in CG
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P
Middle-aged Americans
Body Mass Index (BMI) measured
High BMI
blood glucose
high
low
E
C Low BMI
O
T
cross-sectional study with numerical
measures
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P
Middle-aged American women
Gold Standard
Breast cancer
positive
mammogram
negative
EGO:
likelihood of a positive
mammogram if breast
cancer
E
C
O
no Breast cancer
T
CGO:
likelihood of a positive
mammogram if no
breast cancer
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1st formula:
occurrence = outcomes ÷ population
its all about EGO and CGO
• EGO ÷ CGO = Relative Risk (RR)
• EGO – CGO = Risk Difference (RD)
measures of occurrence: risk; rate; likelihood; probability;
average; incidence; prevalence
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GATE: framework for nonrandom error
2nd acronym: RAMBOMAN
Recruitment
Allocation
Maintenance
Blind
Objective
Measurements
ANalyses
1 picture, 2 formulas & 3 acronyms
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Study setting
RAMBOMAN
Eligible population
recruitment process
P
P
Recruitment of participants
‘who are the findings applicable to?’
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RAMBOMAN: ‘were participants well Allocated to
exposure & comparison groups?’
was Allocation
to EG & CG
successful?
RCT: allocated by randomisation
(e.g to drugs)
Cohort: allocated by
measurement (e.g. smoking)
EG & CG
EG CG
similar at
baseline?
EG CG
O
T
E&C
measures
accurate?
O
T
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P
RAMBOMAN
‘were Participants well Maintained in
the groups they were allocated to?’
EG CG
O
T
completeness of follow-up
compliance
contamination
co-interventions
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P
EG CG
RAMBOMAN
‘were outcomes well Measured?’
were they measured Blind to whether
participant was in EG or CG ?
O
T
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RAMBOMAN
P
‘were outcomes well Measured?’
were they measured Objectively?
EG
CG
O
T
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RAMBOMAN
P
EGA
‘were the ANalyses done well?’
CGA
EGC CGC
If RCT were Intention To Treat (ITT)
analyses done?
b
a
O
T
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P
RAMBOMAN
‘were the ANalyses done well?’
EG CG
adjustment for baseline differences /
confounding?
O
T
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GATE: random error: 2nd formula:
random error = 95% confidence interval
sample from a
population
EGO ± 95% CI
CGO ± 95% CI
There is about a 95% chance that the true value in the underlying
population lies within the 95% CI (assuming no non-random error)
1 picture, 2 formulas & 3 acronyms
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GATE: a framework for error in
systematic reviews & meta-analyses:
3rd acronym: FAITH
1 picture, 2 formulas & 3 acronyms
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systematic review: a study of studies
study sources
studies screened
studies appraised & allocated:
included
excluded
studies summarised
& pooled if
homogeneous
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critical appraisal of SR: FAITH
study sources
Find
studies screened
Appraise
studies appraised & allocated:
Include
included
Total
Heterogeneity?
excluded
studies summarised
& pooled if
homogeneous
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1 picture, 2 formulas & 3 acronyms
GATE: framework for the 4 steps of EBP
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the steps of EBP:
1. Ask
2. Acquire
3. Appraise
4. Apply & Act
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EBP Step 1: ASK - turn your question
into a focused 5-part PECOT question
P
2. Exposure
4. Outcomes
E
yes
no
1. Participants
C
3. Comparison
O
T
5. Time
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EBP Step 2: ACQUIRE the evidence – use
PECOT to help choose search terms
P
Exposure
Outcomes
E
yes
no
Participants
C
Comparison
O
T
Time
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EBP Step 3: APPRAISE the evidence –
with the picture, acronyms & formulas
P
Recruitment
P
Allocation
E
Maintenance
E
C
blind
objective
O
T
C
O
T
Measurements
ANalyses
Occurrence = outcomes ÷ population
Random error = 95% Confidence Interval
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APPLY the evidence by AMALGAMATING the
relevant information & making an evidencebased decision:’ the X-factor
©
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X-factor: making evidence-based decisions
epidemiological
evidence
person
values &
preferences
family
community
system
features
economic
legal
political
patient’s
clinical
circumstances
practitioner
X
Practitioner e pertise: ‘putting it all together’ - the art of practice
Clinical expertise in the era of evidence-based medicine and patient choice. EBM 2002;736-8 (March/April) 49
GATE critically appraised topic
(CATs) forms
find these at:
www.epiq.co.nz
GATE CAT – 4-sheet workbook (in Excel)
sheet 1: GATE-Ask & Acquire
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GATE CAT – 3-sheet workbook (in Excel)
sheet 2: GATE-Appraise (with calculator)
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GATE CAT – 3-sheet workbook (in Excel)
sheet 3: GATE-Apply
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