Transcript Slide 1

Evidence-Base Medicine
How to Practice and Teach EBM
Chapter 5 : Therapy
Vanderbilt Sports Medicine
“4S” Organization of Evidence
Assessing Individual Studies
Are the results VALID ?
Are the results IMPORTANT ?
Are the results APPLICABLE ?
Are The Results Valid?
Was the assignment of patients to
treatment randomized?
- Randomization balances the treatment groups
for prognostic factors
- Mention of randomization usually made in title
or abstract
- If study not randomized, move on to next study,
unless…
… no randomized trials found
Then, options are:
1. Check search methods
2. Determine whether treatment effect is so large
that false-positive results are unlikely (rare)
3. Accept conclusion if study treatment determined
to be useless or harmful
4. Consider “n-of-1” trial
5. Try to find evidence of another management
option
Are The Results Valid?
Was the assignment of patients to
treatment randomized?
Was the randomization concealed?
Were the groups similar at the start
of the trial?
- “Confounders” avoided or adjusted
for
Are The Results Valid?
Was the assignment of patients to treatment
randomized?
Was the randomization concealed?
Were the groups similar at the start of the trial?
Was the follow-up of patients
sufficiently long and complete?
- “Worst case” analysis – 20%
Are The Results Valid?
Was the assignment of patients to treatment groups
randomized?
Was the randomization concealed?
Were the groups similar at the start of the trial?
Was the follow-up of patients sufficiently long and
complete?
Were all the patients analyzed in the
groups to which they were randomized?
- “Intention-to-treat” analysis
Are The Results Valid?
Was the assignment of patients to treatment
randomized?
Was the randomization concealed?
Were the groups similar at the start of the trial?
Was the follow-up of patients sufficiently long and
complete?
Were all the patients analyzed in the groups to
which they were randomized?
Were patients, clinicians, and study
personnel kept blind to treatment?
Are The Results Valid?
Was the assignment of patients to treatment randomized?
Was the randomization concealed?
Were the groups similar at the start of the trial?
Was the follow-up of patients sufficiently long and
complete?
Were all the patients analyzed in the groups to which they
were randomized?
Were patients, clinicians, and study personnel kept blind to
treatment?
Were groups treated equally, apart from
the experimental therapy?
- Prevents “co-interventions” in one group
Are The Valid Results Of This
Individual Study Important?
What is the magnitude of the treatment
effect?
Event = Stroke
5 Years
Control Rate
(CER)
Experimental Rate
(EER)
Relative Risk
Reduction
(RRR)
|CER-EER|/CER
Absolute Risk
Reduction
(ARR)
|CER-EER|
Number Needed
To Treat
(NNT)
1/ARR
5.7%
4.3%
25%
1.4%
(.014)
72
25%
.000014%
(.00000014)
.000057%
.000043%
7,142,857
Are The Valid Results Of This
Individual Study Important?
What is the magnitude of the treatment effect?
How precise is this estimate of the
treatment effect?
- NNTs are estimates of the truth
- Confidence Interval quantifies the
uncertainty in measurement; usually
reported as “95% CI”, meaning the range
of values within which one can be 95%
sure that the true value for the whole
population lies
EBM calculator
www.cebm.utoronto.ca
- “EBM TOOLBOX”
Are The Valid, Important Results Of
This Individual Study Applicable To
Our Patient?
Is our patient so different from those in the study that its results
cannot apply?
Is the treatment feasible in our setting?
What are our patient’s potential benefits and harms from the
therapy? (“decimal fraction”)
What are our patient’s values and expectations for both the
outcome we are trying to prevent and the treatment we are
offering?
- “likelihood of being helped and harmed” (LHH)
LHH =(1/NNT) : (1/NNH)
= 1/72 : 1/5000
= 70 times more likely to be helped than harmed
- LHH may also take into account the decimal fraction
- LHH may also account for patient’s individual, self-assessed
“severity” rating
108 Days Until Kickoff