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