1. Rod Jackson EPIQ group University of Auckland, NZ www.epiq.co.nz
GATE: ‘EBP with pictures’
a Graphic Approach to Teaching EBP
a Graphic Appraisal Tool for EBP
Graphic Architectural Tool for Epidemiology
Rod Jackson
EPIQ group
University of Auckland, NZ
5/9/ Oxford

2. What is evidence-based practice (EBP)?
Policy
‘ways of knowing”
Evidence
Ideally evidence based practice (EBP) involves the integration of evidence (and there are many evidence bases), patient preferences, clinical considerations (practitioner defined issues) and policy issues in making decisions about patients.
Practitioner
Patient

3. What is evidence-based practice?
Policy
‘ways of knowing”
Evidence
However the term evidence based medicine (aka evidence based practice) was coined by a clinical epidemiologist (Gordon Guyatt from MacMaster University in Canada) who challenged clinicians to use more epidemiological evidence when making clinical decisions
Practitioner
Patient

4. What is evidence-based practice?
‘using more evidence from clinical epidemiology (on diagnosis, prognosis & interventions) to inform decisions’
more comprehensively (systematic reviews)
more critically (evidence appraisals)
more quantitatively (probabilities)
Therefore, given its history, the term ebp is more accurately defined as follows.

5. What is the ‘evidence’ of EBP?
‘clinically relevant evidence, sometimes from basic science, but especially from patient-centred clinical research into the accuracy of diagnostic tests*, the power of prognostic markers*, and the efficacy & safety of interventions*’
Modified from Sackett et al. EBM 2nd Edition 2000
* from clinical epidemiological studies

6. Epidemiological evidence is the cornerstone of EBP
‘understanding epidemiological study design is the essential skill for teachers of EBP’

7. The 4 (5) steps of EBP Ask a focussed clinical question
Search for appropriate epidemiological evidence to help answer question
Appraise (critically) the evidence (validity, impact, precision)
Synthesise the evidence with patient, clinical & policy issues; then apply (i.e. answer question)
Assess/ evaluate practice (clinical audit).
Modified from DS et al

8. ‘a tool for modeling the steps of EBP’
CATs:
Critically
Appraised
Topics:
‘a tool for modeling the steps of EBP’

9. Prognosis/Risk (coming) Systematic Reviews (coming)
CAT forms: (in Excel)
Intervention
Diagnosis
Prognosis/Risk (coming)
Systematic Reviews (coming)
download from:

10. The GATE Approach: every epidemiological study hangs on the GATE frame
there is only one study design:
RCT - interventions
Cohort studies - prognosis / interv./ aetiology
Cross-sectional studies - diagnosis
Case-control studies - interv./aetiol.
GATE: Graphic Appraisal Tool for Epidemiology

11. GATE Frame: PECOT Population Exposure Comparison Outcome Time
GATE: Graphic Appraisal Tool for Epidemiology

12. GATE: epi study design (P)
Population P

13. Source Population:
68,561 women screened from 20 outpatients/community screening centres
Eligible Population:
Post-menopausal, established CHD, < 80 yrs, no MI in last 6 mths, no HRT last 3 months P
Participant Population:
all eligibles invited (2763)

14. Comparison (C) [control]
GATE: epi study design (E&C)
Population P
Exposure (E)
[or intervention]
Comparison (C) [control] E C

15. Comparison (C) [control]
HRT
Identical Placebo
Exposure (E)
[or intervention]
Comparison (C) [control] E C

16. GATE: epi study design (O)
Population P
Exposure
Comparison E C a b
yes
Outcomes (O) O no c d

17. 1º CHD E C
yes
Outcomes (O) O no

18. mean HDL cholesterol (mmol/L)
HRT
Placebo
Outcomes (O)
1.4
1.27

19. GATE: epi study design (T)
Population P
Comparison
Exposure E C T
Time (T)
Outcomes O

20. E C T
Time (T) O
CHD measured over 4.1 years (longitudinal)

21. E C T
Time (T) O
HDL cholesterol measured at 1 year (cross-sectional)

22. Multiple Exposure categories Multiple Outcome categories
GATE: epi study design
Population P
Comparison
Multiple Exposure categories E1 E2 E3 C
Multiple Outcome categories

23. GATE: epi study design Population P E Correlation coefficient O ©
Continuous measure of Exposure: e.g. body mass index
high…med..low
Correlation coefficient
low
Continuous measure of Outcomes e.g. lipids O
medium
high

24. non- randomised allocation
Cohort (Follow-up) study: archetypal epidemiological study
Population P
cohort
non- randomised allocation EG CG
Exposure Group
Comparison Group
Real life time T
Time
Outcomes O
ill-health
“Life” is a cohort study: a “natural experiment”

25. Cohort of women diagnosed with breast cancer
Cohort study (prognosis): Danish Breast Cancer Cooperative
Cohort of women diagnosed with breast cancer
Population P
Non-randomised allocation to prognostic groups
No childbirth <2 yrs before diagnosis
childbirth <2yrs before diagnosis EG CG T
10 years
yes death no O
Kroman et al. BMJ 1997;315:851-5

26. Cohort of British Doctors established in 1951
Cohort study (aetiology): British Doctors Study
Cohort of British Doctors established in 1951
Population P
Non-randomised allocation (self-reported smoking) EG CG
Non-smokers
Smokers T
50 years
yes Lung Cancer . no O
Doll et al. BMJ 2004;328:1519

27. Non-randomised allocation (self-reported use)
Cohort study (intervention): Nurses Health Study
Cohort of US Nurses
Population P
Non-randomised allocation (self-reported use) EG CG
No HRT
HRT T
10 years
yes CHD no O
Stampfer et al. NEJM 1991;325:756-62

28. Randomised Controlled Trial (RCT): HERS
Population P
Randomised allocation
Exposure (intervention): HRT
Comparison (control): Placebo EG CG T
Time
Outcomes: CHD O
Hulley et al. JAMA1998;280:605-13

29. No one allocated to Comparison Group
Case series
Population P
Exposure Grp EG C
No one allocated to Comparison Group T
Time
Outcomes O

30. Allocation: randomised or non-randomised
Before-After Study
(& cross-over study)
Population P CG
Comparison Grp
Allocation: randomised or non-randomised EG
Exposure Grp T
Time
Outcomes O

31. Cross-sectional (prevalence) study/survey: PECO
Population P
Real life time O
 LTPA
 angina EG CG
 angina
 LTPA
Time ? O EG CG
E/C assignment & Outcomes assessed in cohort at same Time

32. Allocation by measurement
Diagnostic Test Accuracy Study (cross-sectional)
Population P
Allocation by measurement
EG: Gold Standard +ve
CG: Gold Standard -ve EG CG
Time
GS+
GS-
+ Test Outcomes . - a b O c d

33. Allocation by measurement
Diagnostic Test Study Application (cross-sectional)
Population P
Allocation by measurement
EG: Test +ve
CG: Test -ve EG CG
Time T+ T-
+ve predictive value. a b O c d
-ve predictive value.

34. GATE: the NUMBERS Population P= EG= CG= T= a= b= c= d= ©
Exposure Group
EG=
CG=
Comparison Group
Time T= a= b=
Outcomes c= d=

35. GATE: the numbers = HERS
P= 2763
Population
EG= 1380
CG= 1383
Exposure Group
Comparison Group
Time
a= 172
b= 176
T= 4.1 yrs
Outcomes

36. Denominators = EG x T and CG x T Numerators = a or c and b or d
Occurrence = outcome / population P=
Population
Denominators = EG x T and CG x T
sub-populations
EG=
CG= T + a= b=
Numerators = a or c and b or d
outcomes - c= d=
Epidemiology = numerator / denominator (E=N/D)

37. GATE: occurrence = numerator / denominatorP=
EG=
CG= T=
Exp. Group Occurrence EGO = a / EG x T
Comp. Group Occurrence CGO = b / CG x T a= b= c= d=
EGO = c / EG x T
EGO = d / EG x T

38. GATE: occurrence HERS P= 2763 T= 4.1 yrs EG= 1380 CG= 1383
Exp. Group Occurrence EGO = A / EGxT = 172/1380 x 4.1 = 30.40/1000/yr
A= 172
B= 176
Comp. Group Occurrence CGO = B / CGxT = 176/1383 x 4.1 = 31.04/1000/yr

40. Occurrence = 30.40 / 1000 persons / year = 30.40 / 1000 persons / year
EGO = Exposure Group Occurrence (A/[EGxT])
CGO = Comparison Group Occurrence (B/[CGxT]
= / 1000 persons / year
= / 1000 persons / year

41. Effects: comparing occurrences
Relative Effect/Risk (RR) = EGO
CGO
e.g. relative risk, risk ratio, prevalence ratio, incidence ratio
Absolute Effect/Risk Difference (RD) = EGO - CGO
e.g. risk difference, absolute risk
Number Needed to Treat (NNT) to prevent/cause 1 event = 1/RD

42. Using GATE to frame all the steps of EBP

43. STEP 1: Ask focussed 5-part questions:
1. Participants (patient/population group)
2. Exposure (intervention if about therapy)
3. Comparison (there is always an alternative!)
4. Outcome
5. Timeframe

44. STEP 2: Search for best evidence using 3/4-part search terms:
1. Participants (patient/population group)
2. Exposure (intervention if about therapy)
3. Comparison (e.g placebo)
4. Outcome

45. Step 3a: appraise the evidence - hang the study & numbers on the GATE frame: PECOT
Population P
Exposure
Comparison E C T
Outcome O
Time

46. Step 3b:appraise the evidence: ‘did the right people get in the right places? RAMM
Representative of who? P
Allocated appropriately?
Measured well? -blinded or objective -complete E C T
Measured well? -blinded or objective -complete O

47. R A M M

48. EBCP Step 4: applying the evidence - the X-factor

49. X-factor: making evidence-based decisions
Epidemiologic evidence
Patient preferences
Policy issues
clinical considerations
‘clinical expertise:
other ways of knowing’
X-factor: integrating everything

50. Step 4

51. the evidence based practitioner
RAM

52. a tool for life long learning
the CAT:
a tool for life long learning