Making epidemiological evidence more accessible

using pictures

Rod Jackson

Updated November 09

What is Evidence Based Practice?

What is Evidence Based Practice?

The 6 steps of Evidence Based Practice

1. ASK questions relevant to your clinical problem using the PECOT (PICO) framework

2. ACCESS - search for epidemiological evidence to help answer your questions using the key PECOT terms

3. APPRAISE the evidence for its validity, effect size, precision)

4. AGGREGATE the aggregated (systematically reviewed) evidence with patient/community, clinical/health & policy issues & make an evidence-based decision

5. APPLY (implement) your decision6. [AUDIT your usual practice (i.e. compare your usual

practice for this clinical problem against ‘best’ evidence-based practice) – is there an evidence-practice gap?].

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

P

E C

O

T

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)

P

E C

O

T

EBP Step 2: ACCESS - search for the best evidence to answer your questions

Use the key PECOT components to choose search terms

P

E C

OT

• P

• E

• C

• O

• T

• Recruitment

• Allocation

• Maintenance

• Blind or

• Objective measurements of outcomes

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 (ideally

from a SR)

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

Blind or Objective measurements of

outcomes

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

Blind or Objective measurements of

outcomes

Study appraisal scores

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 processes?P

Study setting & eligibility criteria well described?

e.g. Recruit random/representative sample ORRecruit consecutive eligibles

‘appropriateness’ depends on study question

RAMBO

EG CG

OT

appropriate Allocation process?to EG & CG?

P

Allocation process well described?

If allocated by investigators was it done well?- was allocation random (e.g drugs)and was allocation concealed? ORIf allocated by measurement (e.g. smoking) - were E & C measured well

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 most 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?outcome measurements

P

If outcome measurements not Objective (eg. automated or definitive) were investigators blind to exposure (and comparison exposure)

A

The 4 (GATE) study biases

P

E C

OT

Recruitment bias

Allocation bias

Maintenance bias

Outcome measurement bias

The GATE frame (design & bias)

P

E C

OT

Recruitment

Allocation

Maintenance

Blind or Objective measurement

Participants

Exposure

Comparison

OutcomesTime

The different study designs

illustrated with GATE

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(reference standard +ve)

Test

Disease –ve(reference standard –ve)

a bc d

Likelihood +ve test if D+ve:EGO = a ÷ EG

Likelihood +ve test if D -ve:CGO = a ÷ CG

+

-

EGO/CGO = +ve LR

Diagnostic test accuracy studyP

EG CG

OTest a b

c d

Likelihood -ve test if D+ve:EGO = c ÷ EG

Likelihood -ve test if D -ve:CGO = d ÷ CG

+

-

EGO/CGO = -ve LR

Disease +ve(reference standard +ve)

Disease –ve(reference standard –ve)

Diagnostic test for disease prediction

P

EG CG

O

Test +ve

Disease(reference standard)

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

A CAT documents the steps for a specific question

1. ASK questions relevant to your clinical problem using the PECOT (PICO) framework

2. ACCESS - search for epidemiological evidence to help answer your questions using the key PECOT terms

3. APPRAISE the evidence for its validity, effect size, precision)

4. AGGREGATE the aggregated (systematically reviewed) evidence with patient/community, clinical/health & policy issues & make an evidence-based decision

5. APPLY (implement) your decision6. [AUDIT your usual practice (i.e. compare your usual

practice for this clinical problem against ‘best’ evidence-based practice) – is there an evidence-practice gap?].

CATS (in excel)

Download from www.epiq.co.nz

Some of the CATs need updating

GATE-lite(simple1 page CATs)