Making epidemiological evidence more accessible using pictures Rod Jackson Updated November 09

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 decision 6.[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 GroupComparison Group Outcomes Time 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 EC O T P E C O T Recruitment Allocation Maintenance Blind or Objective measurements of outcomes EBP Step 3: Appraise the evidence using 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

The GATE frame © the shape of every epidemiological study

GATE study design (PECOT) P E C O T

GATE study analyses (EGO & CGO) ab cd EG CG

GATE study appraisal (RAMBO) P E C O T Recruitment Allocation Maintenance Blind or Objective measurements of outcomes

GATE study design (PECOT) Participants Exposure GroupComparison Group Outcomes Time P E C O T

Participants Study Setting Eligible Participants Participants P

Exposure & Comparison Groups Exposure or Intervention Group (EG) Comparison or Control Group (CG) EG CG

Outcomes (O) O ab cd yes no ‘Dis-ease’

Time (T) T incidence prevalence

GATE study analyses

Denominator (Participants) D N Numerator (Outcomes) O = 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 ab cd Numerator 2: b

Occurrence = N ÷ D P EG CG O Denominator 1: Exposure Group EG Numerator 1: a Denominator 2: Comparison Group CG ab cd 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 time P EG CG O Denominator 1: Exposure Group EG x T Numerator 1= a Denominator 2: Comparison Group CG x T ab cd 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 O T 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!’

R AMBO E C O T appropriate Recruitment processes? P Study setting & eligibility criteria well described? e.g. Recruit random/representative sample OR Recruit consecutive eligibles ‘appropriateness’ depends on study question

R A MBO EG CG O T 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? OR If allocated by measurement (e.g. smoking) - were E & C measured well Allocate

EG CG O T P RCT: Allocate randomly by investigators (e.g drugs) EG CG O T P Cohort: Allocate by measurement (e.g. smoking)

RA M BO EG CG O T 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 & CG Contamination low & similar in EG & CG Co-interventions low & similar in EG & CG Completeness of follow-up high & similar in EG & CG

RAM BO EG CG O T 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 O T Recruitment bias Allocation bias Maintenance bias Outcome measurement bias

The GATE frame (design & bias) P E C O T Recruitment Allocation Maintenance Blind or Objective measurement Participants Exposure Comparison Outcomes Time

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 GroupComparison Group Outcomes Time P E C O T 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 GroupComparison Group Outcomes Time P E C O T Allocated by randomisation Best design for investigating treatments

Case series is a Cohort study with no comparison group Participants Exposure Group Outcomes Time P E C O T Allocated by measurement

Before-after study Participants Exposure Group Comparison Group Outcomes Time P C O T Allocated by timing of intervention E

Cross-over trial Participants Exposure Group 2 Comparison Group 2 Outcomes Time P C2C2 O T Allocated by randomisation E2E2 E1E1 C1C1 Exposure Group 1 Comparison Group 1

Cross-sectional study Participants Exposure GroupComparison Group Outcomes Time P E C O T Allocated by measurement real-life time best design for prevalence and diagnostic test accuracy

Diagnostic test accuracy study P EG CG O Disease +ve (reference standard +ve) Test Disease –ve (reference standard –ve) ab cd 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 study P EG CG O Test ab cd 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 ab cd Likelihood of D if test +ve: EGO = a ÷ EG Likelihood of no D if test -ve CGO = d ÷ CG + - Positive predictive valueNegative predictive value

Diagnosis: test accuracy EG CG O Test ab cd + - P P CG EG Disease

Diagnosis: test accuracy EG CG O Test ab cd + - P P CG EG Disease Diagnosis: disease prediction

Case control study for investigating aetiology, interventions when outcomes rare ExposedNot Exposed Cases ab Controls cd

Case control study Exp.Not Exp. Cases ab Controls Participants Exp Group Comparison Group Outcomes Time P EG CG O T cases ‘nested in a virtual cohort study’ ab controls egcg

P Comparison E1E1 C E2E2 E3E3 Multiple Exposure categories Multiple Outcome categories GATE: multiple categories Participants

P Continuous measure of Outcomes e.g. lipids O low 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 decision 6.[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 Some of the CATs need updating

GATE-lite (simple 1 page CATs)