critical reading of medical articles
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Critical Reading of Medical Articles. VOLGOGRAD - October 2011. Pr. Pierre-Emmanuel Falcoz Strasbourg University Hospital. After all, WHY?. Notion of « Evidence Based Medicine » It is not possible to read all the medical literature - PowerPoint PPT PresentationTRANSCRIPT
Critical Reading of Medical Articles
VOLGOGRAD - October 2011
Pr. Pierre-Emmanuel FalcozStrasbourg University Hospital
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After all, WHY?
Notion of « Evidence Based Medicine » It is not possible to read all the medical literature We must learn to retain ONLY good publications
that will modify our medical behavior when faced with a given situation
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Which sources of information?
The « reference » book The « expert » The medical literature
– google: « pubmed »– medline : 20-30 000 articles/month
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Quality criteria of an article
The structure of the article The type of study The methodological quality (internal validity) The practical feasibility (extrapolation)
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The structure of the article
The title:– Interesting, useful and linked to our question
The abstract: – informative– IMRaD structure– One introductory sentence: the objective– 2 or 3 sentences regarding material and methods:
appropriate to the question raised– 3 or 4 sentences illustrating the results: accurate and
relevant– One concluding sentence
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Introduction – The justification – The objective
Material and methods– The patient(s) (inclusion and exclusion criteria)– Description of the method– End point and outcome measure– The plan of the analysis
The structure of the article
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Results– Description of the included patient(s)– They should correspond to patients announced in
the material and methods paragraph– Data should be clear, precise and pertinent– Calculation should be easily tested
Discussion: comparison of the results with those of other articles
Written paragraphs should be well differentiated
do not mix sub-headings!!!
The structure of the article
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The different types of studies
Therapeutic studies Diagnostic studies Prognostic studies Epidemiologic studies Economic studies
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The randomized controlled trials
« The gold standard » enables one to answer the question asked
Only way to obtain reliable proof of the effectiveness of a given treatment
The other types of studies: – Non-randomized prospective trials, retrospective
studies, e.g. …– Lower level of scientific proof
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A short story...
After myocardial infarction, the existence of ventricular extra systoles (VES) increased the risk of sudden death
Class 1 anti-arrhythmics erase VES From this data, such treatments have been given to prevent
sudden death… Without any trials of clinical criteria…
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CAST study (1991)
Death / n mortalityAnti-arrhythmic group 39 / 432 9%Control group 18 / 423 4%
RR=2.13, p<0.05
80 000 Deaths induce by the treatment in the USA– More than Vietnam War (Moore)
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Anti-arrhythmics in post myocardial infarction period
Ventricularextrasystoles Sudden death
Flecaine
Proven
Prov
en
Not confirmed in real settings
by actual findings
Speculative
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Comparative trial
No treatment
Treatment studied
10 %
12 %
Difference = effect of the treatment
End point5-y mortality
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The quantification of scientific proof (ACCP)
Level 1 : •Randomized trials with definitive (unquestionable) results•Meta-analyses
Level 2 :•Randomized trials (low power)•Non randomized controlled trials (well designed)
Level 3 :•Non controlled prospective trials (well designed)
Level 4 : •Controlled trials with bias•Comparative trials (historical series)
Level 5 :•Retrospectives studies or case-series
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The bias
Definition: there is a bias when the difference observed between two groups at the conclusion of the trial is due to a factor other than the studied treatment itself
Population
Randomization
Experimental group Control group
Treated Untreated
Follow-up
Results
Selection bias
Execution bias
Exclusion bias
Detection bias
Follow-up
Results
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The different biases – a summary
Selection bias– Difference in the base prognosis of the patient(s)
Execution bias– difference in follow-up and care given to the patient(s)
Exclusion bias– difference with regard to the “departure” from the studies
Evaluation bias (measure)– difference in evaluation of the end-point
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Comparable groups
Similar groups– Same type(s) of patient(s)– Same stage of the disease, etc…
That are different ONLY due to the applied treatment If a difference exists, it is ONLY due to the treatment
Grp T
Grp C
Treatment
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Composition of groups
The distribution should not depend on:– the patient– the disease– the physician– the medicine
By random drawing of lots:– random allocation– assures that , on average, the 2 groups are strictly comparable
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Poor control groups
Historical controls– For example, patients treated 5 years ago– Those patients are not comparable to those currently
treated
Geographical control– patients of another department
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Statistical reality of the results
An observed difference between 2 groups could be either real or due to chance
Statistical tests allow the statistical reality of the difference to be assessed
The alpha risk is the risk of wrongly drawing a conclusion regarding the effectiveness of a treatment, when in reality this difference is due to chance
this risk is set up to 5% The danger would be to to increase the alpha risk and thus
wrongly conclude that a difference exists between the 2 groups
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Statistical test: interpretation
Observeddifference Test
It is unlikely that the observed difference would be due to chanceSignificant difference
The probability that the observed difference would be due to chance is highNon significant difference
P>5%
P<5%
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Primary endpoint
• Death from all causes
Secondary endpoint
• Cardiovascular death
• Sudden death
• Myocardial infarction
• Cerebrovascular accident
• Surgery
• Death (all causes)
• Cardiovascular death
• Sudden death
• Myocardial infarction
• Cerebrovascular accident
• Surgery
No definition of the primary endpoint
Risk of wrongly drawing a conclusion regarding the
effectiveness of the treatment = 30%
6 statistical tests
Risk of wrongly drawing a conclusion regarding the
effectiveness of the treatment = 5%
A priori definition of a primary endpoint
1 single statistical test
Endpoint
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Test 1
Risk to wrongly conclude to a
difference = 5%
Test 2
Risk to wrongly conclude to a
difference = 5%
Test 4
Risk to wrongly conclude to a
difference = 5%
Test 3
Risk to wrongly conclude to a
difference = 5%
Overall, the risk of wrongly drawing a conclusion regarding a difference when utilizing these four comparisons is much greater than 5%
n overall risk
2 0.10
3 0.13
5 0.23
10 0.40
At dice game, the probablity to obtain one SIX is higher with 3 dices than with only one
Multiple comparisons
Inflation of the alpha risk
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The methodological value of the result
The trial respects the experimental design A hypothesis formulated A PRIORI The entire experimental plan is devised A PRIORI
– the primary endpoint– the calculation of the number of required subjects– an analysis planned
The results should correspond to the formulated hypothesis One cannot draw a conclusion in terms of causality if a result
is not derived from this approach– does not concretely demonstrate anything– at best it suggests an effect
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The clinical relevance
It allows to ascertain that:– The benefit of the treatment is sufficiently important– The clinical criteria is relevant– The ratio benefit/risk is acceptable– The treatment is applicable in daily practice
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The methodological relevance
The main objective is clearly formulated The therapeutic methods are describe with precision:
– the comparison treatment is adapted– the evaluated treatment is applicable in daily practice
The primary endpoint:– Clinical, relevant, validated
The patient(s) included in the trial is/are representative:– the studied population resembles patients seen in daily
practice
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The importance of the therapeutic effect
The fact that the trial is significant (p<5%) is not good enough!!!!
If the therapeutic effect is minimal, it might be of little or no interest to our daily practice…
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The accuracy of the therapeutic effect
The confidence interval Indicates the accuracy of the estimation of the size of the
therapeutic effect A 95% confidence interval assess the range of values within
which we are 95% certain to find the true sought value
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95% confidence interval
0.4 0.6 0.8 1 1.2 1.4
Trial A
Trial B
Trial C
Relative Risk
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The quantification of the therapeutic effect
It allows me to know how much my chances of improvement could be increased if I use this therapeutic !
The relative risk (RR) or the odds ratio (OR) The relative risk reduction (RRR) The absolute risk reduction (ARR) The number needed to treat (NNT)
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The definitions
Relative risk: risk of treated patients in relation to the risk of the control
Relative risk reduction: is the amplitude of the risk reduction Absolute risk reduction: is the absolute value of the risk
reduction The number needed to treat: is the number of patients we
must treat to avoid, on average, one event
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Number needed to treat (NNT)
N. Engl J Med 2004
Surgery Surgery +CT
N.N.T.
2 years 67% 70% 26
5 years 40% 44.5% 18
Interpretation:
At 2 years: we must treat 26 patients by chemotherapy to avoid 1 death !!!
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The benefit / risk ratio
The decision should weigh the beneficial effects against the adverse events– Are the adverse events acceptable?– Do the adverse events offset the totality of the benefit?
The benefit / risk ratio is unfavorable in the following situations:– the seriousness of the adverse events represents an
unacceptable risk with regard to the seriousness of the disease
– the frequency of the adverse events is high– the new therapeutics are less well tolerated than the
available therapeutics
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Practical guide
Evaluation of the internal validity (methodological quality)– the research of bias– the statistical reality of the result– the methodological value of the result
The clinical relevance and the use in daily practice– the objective of the trial– the relevance of the main end point– the representativity of the included patient(s)– the feasibleness of the therapeutic– the size of the therapeutic effect– the benefit / risk ratio
Thank you for your attention!35
The end…