Using evidence in
practice
Nick Price 4th April 2006
Objectives
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To have an overall understanding of the concept of
evidence based practice.
To critique how ‘evidence’ is presented in journals and
by journalists.
Raise awareness of other factors that influence clinical
decision making.
To be able to apply simple statistics in practice.
To be able to present these to patients, minimising bias.
To develop some of the skills in this area required to
pass the MRCGP.
Schedule
1400-1500
Overview of EBP
Panorama programme on Herceptin
.
1515-1530
1530-1615
Tea
Group work
Critically appraising an editorial.
Working out some numbers
Practice explaining risk to patients
1615-1630
Summary and evaluation
(plenary)
What is evidence based practice?
Evidence based medicine?
Maybe it is the application of the best available
scientific knowledge to the patient’s or
population’s clinical problem?
Or
‘Evidence-based medicine is the integration of
best research evidence with clinical expertise and
patient values’ Sackett et al (2000)
A model of influences in
clinical decision making
Science
Social Science Arts and humanities
Ethics
Adaptability, broad perspective
Scientific Method
Counting differences
Understanding differences
Humane Judgement
Technical judgement
Clinical Judgement
Principles of a health care
system
Systematic review
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equity
quantitative
effectiveness
efficiency qualitative
appropriateness
accessibility
responsibility
humanity
Meta-analysis
RCT
Cohort studies
Case control studies
Descriptive studies
Panorama
‘Should I sell my house to pay for
Herceptin, Doctor?’
How would you gather evidence?
First define your question
PICO
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Population
Intervention(s)
Comparison
Outcome.
Levels of evidence
(I-1) a well done systematic review of 2 or more RCTs
 (I-2) a RCT
 (II-1) a cohort study
 (II-2) a case-control study
 (II-3) a dramatic uncontrolled experiment
 (III) respected authorities, expert committees, etc..
(Good Old Boys Sitting Heroically At Tables?)
 (IV)....someone once told me...
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Gathering evidence
Thorough
Practical
Medline search
 SR and Meta-analyses
 RCTs
 Review articles
 Observational Studies
Clinical Evidence
Cochrane
Bandolier
DTB MeReC
RCGP/RCPsych guidelines
NICE guidelines
NSF
Local Guidelines
Ask the consultant or others?
What I actually did for Herceptin
Medline – got nowhere really
 www.scholar.google.com – got nowhere really
 Asked my mates a bit.
 www.bmj.com – editorial and then references
from that.
Could have done what?
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Making sense of numbers
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Relative risk
Absolute risk
Absolute risk reduction / harm
NNT
NNH
Hazard Ratio
Cost per case / QALY
So lies damn lies and statistics?
Absolute risk / benefits often sound small
 Relative risk / benefits can sound big
e.g.
 Your chance of winning the lottery with 2
tickets as opposed to one is increased by 1 in
14million
 Your chance of winning the lottery with 2
tickets as opposed to one is increased by 100%
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Numbers Needed to Treat
The average number of people from a defined
population you would need to treat with a
specific intervention for a given period of time
to achieve one beneficial outcome.
NNT = 1 / ARR
Can you calculate this for winning the lottery
jackpot?
Assume chance of winning is 1 in 14m per ticket
per draw.
NNTs 2
ARI = 1/14m per ticket per draw
= 1/14m x 2 per week with 1 ticket for each
draw
= 1/14m x2 x52 x5 for 5 years
= 520/14m
NNT = 14m/520 = 27,000 approx
i.e. 27,000 people have to buy 2 tickets a week for
5 years for one person to win the jackpot
Summary
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Trials are there to inform clinical decision
making.
Identifying appropriate literature needs to
consider quality / rigour but also practicality.
Some stats are really quite easy but need to be
used with care if you are to be honest.
I suggest that risks and benefits should be
expressed in both absolute terms and relative
terms and DON’T mix them up!
Some reading / resources:
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Greenhalgh T (2000) How to Read a Paper:
The basics of evidence based medicine.
London BMJ Publishing
McGovern D P B, Summerskill W S M,
McManus R (2001) Evidence-based medicine
in General Practice. Oxford BIOS Scientific.
OR
Sackett DL, Strauss S, Richardson WS,
Rosenberg W, Hayes RB (2000) Evidencebased Medicine: How to practice and Teach
EBM. Edinburgh Churchill Livinstone
Tea time
Then:
Reviewing the editorial and doing some sums.
Back here for 1615 for close and evaluation