GATE: Graphic Approach To Epidemiology
Rod Jackson
2013
1 picture, 2 formulas & 3 acronyms
1
The GATE frame:
• Graphic Appraisal Tool for Epidemiological
studies – a framework for appraising studies
• Graphic Architectural Tool for Epidemiological
studies – a framework for designing studies
Presentation outline
1. a framework for study design
2. a framework for study analysis
3. a framework for study error
4. a framework for practicing EBP
1 picture, 2 formulas & 3 acronyms
1. GATE: design of epidemiological studies:
the picture & 1st acronym: PECOT
every epidemiological study can be hung on the GATE frame4
GATE Frame picture
a cohort of British doctors
smoking status measured (observed)
smokers
lung cancer
events counted
yes
no
non-smokers
follow for 10
years
longitudinal (cohort or follow-up ) study
observational studies: allocated to groups by measurement
5
1st acronym: PECOT
P
British doctors
Population/Participants
smoking status measured
Exposure
smokers
Outcomes
Lung cancer
yes
no
E
C
Comparison
non-smokers
O
T
Time
10 years
6
GATE Frame picture & 1st acronym
P
cohort of British doctors
randomly allocated to aspirin or placebo
aspirin
heart attacks
counted
yes
no
E
C
placebo
O
T
follow for 5
years
randomised controlled trial
RCT: allocated to E & C by randomisation process
7
GATE Frame picture & 1st acronym
P
Middle-aged Americans
Body mass index measured
overweight
Diabetes status
measured in all
participants
yes
no
E
C
‘normal’ weight
O
T
Cross-sectional (prevalence) study
8
GATE Frame picture & 1st acronym
P
Middle-aged Americans
Body mass index measured
Diabetes
yes
preno
overweight
obese
E1 E2 C
‘normal’ weight
O
T
Cross-sectional study
(multiple categories)
9
GATE Frame picture & 1st acronym
P
Middle-aged Americans
Body Mass Index (BMI) measured
High BMI
E
C Low BMI
high
mean (average) Blood glucose
low
O
T
Cross-sectional study
(with numerical outcome)
10
GATE Frame picture & 1st acronym
P
Middle-aged American women
Receive Mammogram screening Test
Mammogram positive
E
C
Mammogram negative
yes
O
Breast cancer
no
T
Diagnostic (prediction) study
11
2. GATE: analysis of epidemiological studies:
the 1st formula: outcomes ÷population
the numbers in every epidemiological study can be hung on
12
the GATE frame
1st formula: Occurrence of outcomes =
number of outcomes ÷ number in population/group
British doctors
P
Participant Population
smoking status measured
Exposed Group
EG CG Comparison Group
smokers
Outcomes
Lung cancer
non-smokers
yes
no
a
O
b
T
Time
10 years
13
1st formula: occurrence = outcomes ÷ population
P
British doctors
Population
smoking status measured
Exposed Group
EG CG Comparison Group
smokers
Outcomes
Lung cancer
non-smokers
yes
no
a
O
b
T
Time
10 years
Exposed Group Occurrence (EGO) = a÷EG
= number of outcomes (a) ÷ number in exposed population (EG)
14
1st formula: occurrence = outcomes ÷ population
P
British doctors
Population
smoking status measured
Exposed Group
EG CG Comparison Group
smokers
non-smokers
yes
Lung cancer
no
a
O
b
Outcomes
T
Time
10 years
Comparison Group Occurrence (CGO) = b÷CG
= number of outcomes (b) ÷ number in comparison population (CG)
15
goal of all epidemiological studies is to measure (&
compare) the occurrence of outcomes in (different)
populations (EGO compared with CGO)
P
British doctors
smoking status measured
smokers
yes
EGO:
Occurrence (risk) of
cancer in smokers
EG
a
CG non-smokers
O
b
no
Lung cancer
10 years
T
CGO:
Occurrence of cancer
in non-smokers
16
goal of all epidemiological studies is to measure (&
compare) the occurrence of outcomes in (different)
populations (EGO compared with CGO)
P
British doctors
Randomly allocated to aspirin or placebo
EG
aspirin
yes
EGO:
Occurrence of MI if
taking aspirin
no
a
CG
O
b
placebo
5 years
T
Heart attack (MI)
CGO:
Occurrence of MI if
not taking aspirin
17
goal of all epidemiological studies is to measure (&
compare) the occurrence of outcomes in (different)
populations (EGO compared with CGO)
P
Middle-aged Americans
Body Mass Index (BMI) measured
High BMI
EGO:
high
Average blood glucose
low
in EG
EG CG
O
Low BMI
CGO:
Average blood glucose
in CG
EGO = sum of all glucose levels in EG ÷ number in EG
18
goal of all epidemiological studies is to measure (&
compare) the occurrence of outcomes in (different)
populations (EGO compared with CGO)
P
Middle-aged American women
receive Mammogram screening Test
mammogram positive
yes
EGO:
Occurrence of cancer
if mammogram +ve
EG
CG
a
b
O
no
Breast cancer
mammogram negative
T
CGO:
Occurrence of cancer
if mammogram -ve
19
comparing EGO & CGO
• Risk Ratio or Relative Risk (RR) = EGO ÷
CGO
• Risk Difference (RD) = EGO – CGO
• Number Needed to Treat/’expose’ (NNT)
= 1 ÷ RD
its all about EGO and CGO
Measures of occurrence include: risk; rate; likelihood;
probability; average; incidence; prevalence
3. GATE: identifying where errors occur in epi
studies: the 2nd acronym: RAMBOMAN
Recruitment
Allocation
Maintenance
Blind
Objective
Measurements
ANalyses
GATE frame with RAMBOMAN can be used to identify risk
of error in most/all epidemiological studies
21
Study setting
RAMBOMAN
Eligible population
recruitment process
P
P
were Recruited participants
relevant to the study objectives?
who are the findings applicable to?
22
RAMBOMAN: how well were participants Allocated
to exposure & comparison groups?
was Allocation
to EG & CG
successful?
RCT: Allocated by randomisation
(e.g to drugs)
EG & CG
similar?
T
Cohort: Allocated by
measurement (e.g. smoking)
EG CG
EG CG
O
O
T
E&C
measures
accurate?
23
P
EG CG
O
T
RAMBOMAN
how well were Participants
Maintained in the groups they were
allocated to (i.e. to EG & CG)
throughout the study?
completeness of follow-up
compliance
contamination
co-interventions
24
P
EG CG
RAMBOMAN
Were outcomes measured
blind to whether participant
was in EG or CG ?
O
T
25
RAMBOMAN
P
Were outcomes measured
Objectively?
EG
CG
O
T
26
P
RAMBOMAN
Were the Analyses done
appropriately?
EG CG
Adjustment for confounding
O
T
27
RAMBOMAN
P
EGA
CGA
EGC CGC
Were the Analyses done
appropriately?
Intention to treat?
b
a
O
T
28
the 2nd formula:
random error = 95% confidence interval
EGO ± 95% CI
CGO ± 95% CI
There is about a 95% chance that the true value of EGO & CGO (in the
underlying population) lies somewhere in the 95% CI (assuming no
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non-random error)
the 3rd acronym: FAITH
Critically appraising a systematic review
• Find – were all potentially relevant studies found?
• Appraise – were studies appraised for validity?
• Include – were only appropriate studies included
in the final analyses?
• Total-up – were studies pooled appropriately?
• Heterogeneity – were studies too heterogeneous
(i.e. too different) to pool?
4. GATE : a framework for the 4 steps of EBP
the steps of EBP:
1. ask
2. access
3. appraise
4. apply
[5. audit your practice]
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
33
EBP Step 2: ACCESS the evidence – use
PECOT to help choose search terms
1.
2.
3.
4.
5.
Participants
Exposure
Comparison
Outcome
Time frame
34
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
35
EBP Step 4: APPLY the evidence by
AMALGAMATING the relevant information &
making an evidence-based decision:’ the X-factor
©
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)
6-page GATE CATs (word docs)
39
1-page GATE Calculators (excel files)
40
1-page GATE-lites (writeable pdf files)
all forms on Cecil EBM site
41
extra slides
GATE Frame picture & 1st acronym
P
smokers
E
C
non-smokers
smoking status measured
cases
yes
O
Lung cancer
controls T
no
Case-control study
Observational study: allocated by measurement
44
GATE Frame picture & 1st acronym
P
Middle-aged American women
Measured with ‘gold standard’ for breast cancer
Breast cancer positive
E
C
Breast cancer negative
positive
O
Mammogram
negative
T
Diagnostic test accuracy study
45
The goal of all epidemiological studies is to measure
(& compare) the occurrence of outcomes in
(different) populations (EGO compared with CGO)
P
Middle-aged American women
Measured with gold standard for
breast cancer
Breast cancer
EG
CG
No breast cancer
positive a O b
EGO:
T
Likelihood of +ve
Mammogram if negative
breast cancer
Mammogram
CGO:
Likelihood of +ve
Mammogram if no
breast cancer
46
1st formula (with time):
occurrence = (outcomes ÷ population) ÷ Time
P
British doctors
Population
smoking status measured
Exposed Group
EG CG Comparison Group
smokers
Outcomes
Lung cancer
non-smokers
yes
no
a
O
b
T
Time
10 years
EGO = (a ÷ EG) during time T (a measure of cumulative incidence)
EGO = (a ÷ EG) ÷ T (a measure of incidence rate)
47
1st formula (with time):
occurrence = (outcomes ÷ population) ÷ Time
P
Middle-aged American women
Receive Mammogram screening Test
Mammogram positive
yes
EGO:
Occurrence of cancer
if mammogram +ve
EG
CG
a
b
O
no
Breast cancer
Mammogram negative
T
CGO:
Occurrence of cancer
if mammogram -ve
EGO = (a ÷ EG) at time T (a measure of prevalence)
48