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WELCOME TO THE EVIDENCE BASED MEDICINE
TASK TEAM
Leader:
Howaida
Hashim Ph.D. ELD (ABB)
Coordinator:
Haifa Wahbi
MD. MRCOG
AIM:
Our aim is to
improve patient care by developing and
promoting evidence-based health care,
and to provide support and resources to
anyone who wants to practice or teach
EBM. We have several resources to help
with learning and using EBM.
Contact us.
What is
EBM:
The most
common definition of Evidence Based-
Medicine (EBM) is taken from Dr. David
Sackett. EBM is "the conscientious,
explicit and judicious use of current
best evidence in making decisions about
the care of the individual patient. It
means integrating individual clinical
expertise with the best available
external clinical evidence from
systematic research." (Sackett D, 1996)
EBM is the
integration of clinical expertise,
patient values, and the best evidence
into the decision making process for
patient care. Clinical expertise refers
to the clinician's cumulated experience,
education and clinical skills. The
patient brings to the encounter his or
her own personal and unique concerns,
expectations, and values. The best
evidence is usually found in clinically
relevant research that has been
conducted using sound methodology.
(Sackett D, 2002)
The
evidence, by itself, does not make a
decision for you, but it can help
support the patient care process. The
full integration of these three
components into clinical decisions
enhances the opportunity for optimal
clinical outcomes and quality of life.
The practice of EBM is usually triggered
by patient encounters, which generate
questions about the effects of therapy,
the utility of diagnostic tests, the
prognosis of diseases, or the etiology
of disorders.
Evidence-based medicine requires new
skills of the clinician, including
efficient literature searching, and the
application of formal rules of evidence
in evaluating the clinical literature.
The
practice of EBM is achieved by:
(1)
Converting the need for information into
answerable questions;
(2)
Tracking down the best evidence with
which to answer these questions;
(3)
Critically appraising the evidence for
validity, importance, and applicability;
(4)
Integrating this appraisal with our
clinical expertise and our patient’s
unique biology, values and
circumstances; and
(5)
Evaluating our effectiveness and
efficiency in executing steps 1 to 4 and
finding ways to improve them for the
future.
Recent
developments that have made the practice
of EBM more attainable include
international groups reviewing the
literature, development of
evidence-based journals, availability of
improved search strategies and
electronic search services.
One of the
biggest problems with EBM is simply the
difficulty in quantifying clinical
outcomes. All areas of clinical
practice, including reproductive
medicine, suffer from the lack of good
outcomes data. Clinical research is
often deficient and most physicians have
a limited understanding of interpreting
the literature and optimizing the use of
the data. For example, it is necessary
to know the different types of study
designs and their limitations. The US
Preventive Services Task Force rating
scale for experimental design is either
a randomized controlled trial (I) or a
nonrandomized controlled trial (II-1).
Observational studies are cohort or
case-control studies (II-2), multiple
time series before and after
intervention (II-3) or descriptive
studies, consensus panel, or expert
opinion (III).
Evidence-based medicine has its
limitations. First, no studies have
conclusively proven in a prospectively
randomized trial that EBM has an effect
on outcomes, because no one has overcome
the problems of study design, size and
follow-up that would be necessary. The
principles of evidence-based medicine
can be misapplied and the literature
misinterpreted. Quantifying outcomes can
be difficult, instruments can read
incorrectly, measurements by the
investigator are potentially biased,
statistical significance can be confused
with clinical relevance, data can be
limited or not available when it is
needed, multiple step algorithms are
complex and publication bias can limit
the reporting of negative outcomes.
But studies
have shown that those patients who have
evidence-based therapy have better
outcomes than those who do not. Clinical
protocols for standardizing care have
also been shown to be an effective tool
to improve quality and efficiency of
care. Better methods to provide more
informed consent to patients given the
many variables and personal perspectives
are needed, and more sophisticated
interactive information systems are
needed.

The Steps in the EBM Process:
|
The
patient |
1.
Start with the patient -- a
clinical problem or question
arises out of the care of the
patient |
|
The
question |
2.
Construct a well built clinical
question derived from the case |
|
The
resource |
3.
Select the appropriate
resource(s) and conduct a search |
|
The
evaluation |
4.
Appraise that evidence for its
validity (closeness to the
truth) and applicability
(usefulness in clinical
practice) |
|
The
patient |
5.
Return to the patient --
integrate that evidence with
clinical expertise, patient
preferences and apply it to
practice |
|
Self-evaluation |
6.
Evaluate your performance with
this patient |

Why is EBM important?
Information Needs
Studies of
information-seeking habits of
physicians, have shown that when asked,
physicians reported that their practice
generated about 2 questions for every 3
patients. Only 30% of physicians'
information needs were met during the
patient visit, usually by a colleague.
Reasons for not using printed resources
included office textbook collections too
old, lack of knowledge of appropriate
resources, and lack of time to find the
needed information. (Covell DG, 1995)
When
actually observed, investigators found
that physicians had about 5 questions
for each patient. 52% of these question
could be answered by the medical record
or hospital information system. 25%
could have been answered by published
information resources such as textbooks
or MEDLINE. (Osheroff JA, 1991)
However,
studies have also shown that when
clinicians have access to information,
it changes their patient care management
decisions.
In 1998,
Dr. David Sackett, using an "evidence
cart" on rounds, reported that of 71
information searches to answer clinical
questions, 37 (52%) confirmed the
management decision, but 18 (25%) lead
to a new therapy or diagnostic test and
16 (23%) corrected a previous plan.
(Sackett D, 1998)
Similar
results were report by Crowley et al in
2003. The CAR study showed that of 520
clinical questions for which answers
were sought in the medical literature,
in 53% of these cases the literature
confirmed the management decision, but
in 47% of these cases the literature
changed the medication, diagnostic test,
or prognostic information given to the
patient. (Crowley S, 2003)

The EBM Process
|
The
Patient |
1.
Start with the patient: a
clinical problem/ question
arises out of the care of the
patient. |
|
The
Question |
2.
Construct a well-built question
derived from the case.
|

Glossary of Terms
Absolute
risk and its reduction
This is the
percentage of subjects in any group or
sub-group that experiences a discrete
bad outcome such as death or admission
to the hospital. An efficacious therapy
serves to reduce that risk. For example,
if 15% of the placebo group died and 10%
of the treatment group died, the
absolute reduction in the risk of death
is 5%.
Accuracy
The
proportion of all test results
(positives and negatives) which agreed
with the gold standard.
Applicability (also called external
validity, generalizability, relevance)
This is the
degree to which the results of an
observation, study, or review are likely
to hold true in your practice setting.
Bayes'
Theorem
This is a
simple formula that says that if a
particular test result is
twice as likely to occur in
patients with a disease, condition, or
injury than in patients without, then,
it is twice as likely that the patient
with the result being tested for
actually has the disease as compared to
any randomly selected similar patient
who has not been tested. If you don't
like thinking about things like this,
just use the nomogram in the users
guides or the calculator on the
diagnosis appraisal page.
Bias
This is any
factor which might change the results of
a study from what they would have been
if that factor were NOT present. The
direction of bias may be unpredictable.
For example, giving a team a ten point
advantage might seem to give that side
an advantage but some teams actually
play much better when they have to come
from behind! The validity of a study is
integrally related to the likelihood
that the results have been biased by
factors extraneous to the study design.
Blinding
The
"masking" or concealment from study
subjects, caregivers, or others involved
in the study of any detail(s) of the
study which could introduce Bias. For
example, not telling patients or doctors
which patient gets placebo or actual
drug; or not telling radiologists the
clinical assessment of patients whose
films they are reading.
Case-control study
This might
be considered a randomized controlled
trial played backwards. People who get
sick or have a bad outcome are
identified and "matched" with people who
did better. Then, the effects of the
therapy or harmful exposure which might
have been administered at the start of
the trial are evaluated. In other words,
you first find the people who did poorly
and then look at the therapy or exposure
and compare it to people who didn't get
the therapy. Needless to say, this is a
crude way of doing a study. When the
effect of interest is HARM, this may
actually be the only ethical way of
doing the study.
Case report
This
includes single case reports and
published case series'. These are
searchable as a separate category in the
MEDLINE database
C.A.T.
see
critically appraised topic
Clinical
significance
Results are
clinically significant when they make
enough difference to you and your
patient to justify changing your way of
doing things. For example, a drug which
is found in a megatrial of 50,000 adults
with acute asthma to increase FEV1 by
only 0.5% (P value<.0001) has failed
this test of significance.
Cochrane
Collaboration
An
international organized effort to
organize all existing clinical studies
into systematic reviews easily
accessible to practicing clinicians and
to otherwise facilitate the process of
bringing clinical evidence to bear on
decision making in patient care.
Cohort
study
Also called
a "prospective observational study",
this design follows a group of patients,
called a "cohort", over time to
determine general outcome as well as the
outcomes of different subgroups.
Co
intervention
A therapy
or other ancillary treatment which is
NOT under investigation which is given
to study patients.
Confidence
intervals
An interval
around an observed parameter such as
relative risk which is guaranteed to
include the true value to some level of
confidence (usually 95%). That level of
confidence is only justified to the
extent that bias is absent from the
study. A well known election poll
advertises itself "this poll is accurate
to within 2 percentage points 99% of the
time." This is a way of saying, in
language aimed at voters (perhaps a
skewed sample from the standpoint of IQ)
that the 99% CI around the reported
percentages is
+
2.
Controlled
clinical trial
Any study
which compares two groups by virtue of
different therapies or exposures
fulfills this definition.
Critical
appraisal
The process
of assessing and interpreting evidence
systematically considering its validity,
results, and relevance.
Critically
appraised topic (C.A.T.)
A 1 or 2
page summary of a search and critical
appraisal of the literature related to a
focused clinical question. This summary
should be kept in an easily accessible
place so that it can be used to help
make clinical decisions.
Dichotomous
outcome
Any outcome
measure in which there are only two
possibilities, like dead/alive,
admitted/discharged, graduated/sent to
glue factory. Beware of potentially fake
dichotomous outcome reports such as
"improved/ not improved", particularly
when derived from continuous outcome
measures.
Double
blind
A single
blind study means that someone (patient
or physician) does not know what is
going on. Double blind means that at
least two people (patient and physician)
don't know what's going on. Triple blind
might mean that the paper is written
before the results are tabulated. The
whole point is to prevent bias.
Effect size
The
difference in measured outcomes
attributed to a therapeutic
intervention. This term is encountered
in meta-analyses when different studies
have measured different things.
Effectiveness
I buy a BMW
which test drives miraculously on the
dealer’s special runway. I then find
that the roads in the area where I live
have all been closed. This is a
breakdown of effectiveness. See
efficacy.
Efficacy
The BMW I
have selected for a test drive blows all
four tires, stalls out and crashes on
the dealer’s special runway. I spend two
days in the hospital. This is a
breakdown in efficacy. See
effectiveness.
Event rate
This is a
term for absolute risk.
Exposure
Anything
you can be exposed to: a drug, a
surgical procedure, time, sexual
harassment, rounds, even a diagnostic
test. Most commonly encountered in
therapy, prognosis or harm studies where
the EFFECT of an "exposure" is the
subject of the study.
External
validity
See
applicability.
Generalizability
See
applicability.
Gold
standard
No longer
relevant in the realm of high finance
from whence it originated, this term
gained new life when it was decided that
it should refer to a reference standard
for evaluation of a diagnostic test. For
the purposes of a study, the "gold
standard" test is assumed to have 100%
sensitivity and specificity. This may
well constitute an exaggerated estimate
of the reference test. Choice of the
"gold standard" must therefore be
evaluated in appraising a diagnosis
study.
Harm-Benefit Line
On a graph
of outcomes, this line divides results
favoring therapy from results favoring
the control.
Heterogeneity
Also called
"homogeneity" but having nothing to do
with sexual preference, this term is
used to designate a statistical test
used to determine whether results from a
set of independently performed studies
on a particular question are similar
enough to make statistical pooling
valid. Are the apples sufficiently red
and the oranges sufficiently green to be
able to add them up and report the total
number of "orpples"? As in other
matters, statistical tests do not
guarantee clinical relevance.
Homogeneity
See
heterogeneity.
Incidence
The
rate
at which an event occurs in a defined
population over time. To be
distinguished from prevalence.
Intention-to-treat
Intentions... that with which the path
to hell is lined. Patients assigned to a
particular treatment group by the study
protocol should be retained in that
group for the purpose of analysis of the
study results no matter what happens.
Patients redefined or dropped from a
study early on as a result of protocol
violations unlikely to create bias may
validly be considered exceptions to this
rule.
Internal
validity
See
validity.
Likelihood
Ratio
An operator
defined as the percentage of patients
positive by gold standard for a
particular disease, condition or injury
who have a particular test result
divided by the percentage of patients
without the problem who have that same
test result. A likelihood ratio of two
means that the test result in question
is twice as likely to come a patient
with the problem as it is from a patient
without the problem. The LR may be
derived from reported sensitivity and
specificity or from a clear
understanding of the above definition.
To see how the LR is used, see Bayes‘
Theorem; to actually use it, see the
nomogram. To see how the Likelihood
Ratio is generated, use the calculator
Meta-analysis
A review of
a focused clinical question following
rigorous methodological criteria and
employing statistical techniques to
combine data from independently
performed studies on that question. To
learn more, see the User’s Guide.
Nomogram
for Likelihood Ratio

Null
hypothesis
What do you
do when you want others to be maximally
impressed with what you do? You DECREASE
EXPECTATIONS, then what you do
accomplish looks even better! The null
hypothesis is the assumption that there
is no difference between the groups and
that the treatment you are studying has
no effect. Any difference in outcome
actually observed between the groups is
then evaluated in relationship to the
"zero expectation" hypothesis.
Number
needed to treat (NNT)
The number
of patients who must receive a
particular therapy for one to benefit.
You might tell a patient that an NNT of
10 means that the chance that he/she
will benefit in this way from the
treatment is 1 in 10. To calculate NNT
use the calculator.
Observational study
Any study
of therapy, prevention or harm in which
the exposure is not
assigned to the individual subject by
the investigator(s). A synonym is
"non-experimental"; examples are
case-control and cohort
studies.
Odds ratio
The odds of
an event, understood best by those who
enjoy wagers, is the number of times it
occurred (a) divided by the
number of times it didn’t (b), or
a/b. This contrasts with the
probability of an event which is the
number of times it occurred divided by
the number of times it
could
have occurred, or a/a+b. The odds
ratio is the ratio of the odds of an
event in one group divided by the odds
in another group. When the event
rate or absolute risk
in the control group is small (less than
20% or so), then the odds ratio is very
close to the relative risk.
Placebo
The thing
you give a study subject who has been
assigned to the control group to make
them think they are getting the
treatment you are studying.
Point
estimate
The exact
result that has been observed in a
study. The confidence interval tells you
the range within which the result is
likely to lie.
Post-test
probability
The
likelihood that your patient has the
disease, condition or injury you are
testing for at the moment the result of
the test you (or someone) ordered is
delivered to you. To calculate it you
need the pretest probability or
prevalence and also the likelihood ratio
for the test in question. To do this,
you could use Bayes theorem or, if you
are lazy (and practical), use the
nomogram.
Pre-test
probability
At the
point you order a diagnostic test, you
already have some idea of how likely
your patient is to have the disease,
condition or injury in question. You
think of this as small, medium or large.
"Pretest probability" means putting a
number on the estimate you have already
made. A difference of 10% in either
direction will not change the effect of
the diagnostic test. Putting the number
on your clinical estimate will, however,
allow you to determine what the test
result means, should you want to know.
This is also called prevalence.
Prevalence
The
proportion of people in a defined group
who have a disease, condition or injury.
In the context of diagnosis, this is
also called "pre-test probability." To
be distinguished from incidence.
Prospective
study
Any study
done forwards in time. This is
particularly important in studies on
therapy, prognosis or harm, where
retrospective studies make hidden biases
very likely.
Publication
bias
A possible
bias which can effect systematic
overviews to the extent that studies on
the question at hand with conflicting
results may not have been published.
P value
The
probability that the difference(s)
observed between two or more groups in a
study would occurred if there were no
differences between the groups other
than those created by random selection.
The assumption underlying the p-value is
the null hypothesis.
Power
The chance
that an experimental study will
correctly observe a statistically
significant difference between the study
groups. This may be considered the
"sensitivity" of the study trial itself
for detecting a difference when it is
there.
Randomization
A technique
which gives every patient an equal
chance of winding up in any particular
arm of a controlled clinical trial.
Randomized
Controlled Trial
A
controlled clinical trial in which the
study groups are created through
randomization.
Relative
risk and its reduction
The
probability of an event in one group
divided by the probability of the same
event in another group. Generally the
event is a bad one and the rate in the
therapy group (when it is a therapy
study) is in the numerator. When a
benefit has been observed, this ratio is
less than one. Subtracting the ratio
from one gives the relative risk
reduction, which is the percentage by
which the risk in the control group has
been reduced by the therapy.
Reliability
Sometimes
used loosely, this actually refers to
the reproducibility of a measurement
procedure. It is NOT
the same as validity or
applicability of a study.
Retrospective study
Any study
in which the outcomes have already
occurred before the study has begun.
Risk factor
Any aspect
of an individual’s life, behavior or
inheritance which increases the
likelihood of a disease, condition or
injury.
Sensitivity
The
probability that a patient with a
disease, condition or injury will test
positive by a particular test for the
problem.
Sensitivity
analysis
An
analytical procedure to determine how
the results of a study would change if
the facts were different or different
studies included. This is chiefly
important in meta-analysis or complex
techniques such as decision analysis and
cost-effectiveness analysis.
Specificity
The
probability that patients without a
particular disease, condition or injury
will test negative for the problem by a
particular test.
Statistical
power
see Power
Statistical
significance
A measure
of how confidently an observed
difference between two or more groups
can be attributed to the study
interventions. The p value is the most
commonly encountered way of reporting
statistical significance. The methods
assume that the study is free of bias.
Clinical significance is entirely
independent from statistical
significance.
Stratified
randomization
A way of
ensuring that the different groups in an
experimental trial are balanced with
respect to important factors which could
effect outcome.
Spectrum
In a
diagnosis study, the range of clinical
presentations and of relevant disease
advancement exhibited by the subjects
included in the study.
Systematic
overview
A formal
review of a focused clinical question
based on a comprehensive search strategy
and structured critical appraisal.
Threshold
Probabilities
The level
of suspicion at which your clinical
decision changes
Utility
Particularly for a diagnostic test, this
is a measure of whether the patient is
truly better off as a result of the
test. A test could have high
sensitivity, specificity and good
likelihood ratios and still have low
utility if it is very invasive or poses
other risks or inconvenience to the
patient. It belongs under the section of
a diagnostic review.
Validity
The degree
to which the results of a study are
likely to be true, believable and free
of bias. This is entirely independent of
the precision of the results (p value)
and does not predict the of the results
to your patients.

REFERENCES:
Bordley DR.
Evidence-based medicine: a powerful
educational tool for clerkship
education. American Journal of
Medicine. 102(5):427-32, 1997 May.
Covell, DG.
Uman, CG. Manning, PR. Information needs
in office practice: are they being met?
Annals of Internal Medicine
103(4):596-599, Oct 1995.
Crowley SD,
Owens TA, Schardt CM, Wardell SI,
Peterson J, Garrison S, Keitz SA. A
Web-based compendium of clinical
questions and medical evidence to
educate internal medicine residents.
Acad Med 78(3):270-4, 2003 Mar.
Michaud G.
McGowan JL. van der Jagt R. Wells G.
Tugwell P. Are therapeutic decisions
supported by evidence from health care
research? Archives of Internal
Medicine158(15):1665-8, 1998 Aug
10-24.
Osheroff
JA. Forsythe DE. Buchanan BG. Bankowitz
RA. Blumenfeld BH. Miller RA.
Physicians' information needs: analysis
of questions posed during clinical
teaching. Annals of Internal Medicine
114(7):576-81, 1991 Apr 1.
Sackett, D.
Evidence-based Medicine: How to
Practice and Teach EBM. 2nd edition.
Churchill Livingtone, 2000.
Sackett, D.
Evidence-based Medicine - What it is and
what it isn't.
http://www.cebm.net/ebm_is_isnt.asp
1996.
Sackett DL,
Straus SE. Finding and applying evidence
during clinical rounds: the "evidence
cart". JAMA 280(15):1336-8,
1998 Oct 21.
Tonelli,
M.R. The philosophical Limits of
Evidence-based Medicine. Academic
Medicine 73(12):1234-1240, Dec 1998.
Well-Built Clinical Question
Richardson
WS, Wilson MC, Nishikawa J, Hayward RSA.
The well-built clinical question: a key
to evidence-based decisions. ACP
Journal Club. Nov-Dec 1995;123;A12.

The Literature Search
Duke
University, Medical Center, Ovid
tutorial.
http://www.mclibrary.duke.edu/training/ovid
PDQ
Evidence-Based Principles and Practice,
1999, by
Ann McKibbon, as a reference in search
strategies for doing a literature search
using MEDLINE, CINAHL Database of
Nursing and Allied Health Literature,
PsycINFO, and EMBASE/Excerpta MEDICA.
Order information from B.C. Decker, Inc.
at
http://www.bcdecker.com
UNC-Chapel Hill,
HSL, Database Searching learning module:
http://www.hsl.unc.edu/services/tutorials/srchdbs/splash.htm

Evaluating the Evidence
Users'
Guides to the Medical Literature
from JAMA:
Note: The full text of the Users' Guide
series is available from the
Centre for Health Evidence.
Guyatt GH ;
Rennie D. Users' guides to the medical
literature [editorial]. JAMA 1993 Nov 3;
270(17):2096-7.
Oxman AD ;
Sackett DL ; Guyatt GH. Users' guides to
the medical literature. I. How to get
started. The Evidence-Based Medicine
Working Group. JAMA 1993 Nov 3;
270(17):2093-5.
Therapy
Guyatt GH ;
Sackett DL ; Cook DJ. Users' guides to
the medical literature. II. How to use
an article about therapy or prevention.
A. Are the results of the study valid?
Evidence-Based Medicine Working Group.
JAMA 1993 Dec 1;270(21):2598-601.
Guytt GH ;
Sackett DL ; Cook DJ. Users' guides to
the medical literature. II. How to use
an article about therapy or prevention.
B. What were the results and will they
help me in caring for my patients?
Evidence-Based Medicine Working Group.
JAMA 1994 Jan 5; 271(1):59-63.
Diagnosis
Jaeschke R
; Guyatt G ; Sackett DL. Users' guides
to the medical literature. III. How to
use an article about a diagnostic test.
A. Are the results of the study valid?
Evidence-Based Medicine Working Group.
JAMA 1994 Feb 2;271(5):389-91.
Jaeschke R
; Guyatt GH ; Sackett DL. Users' guides
to the medical literature. III. How to
use an article about a diagnostic test.
B. What are the results and will they
help me in caring for my patients? The
Evidence-Based Medicine Working Group.
JAMA 1994 Mar 2; 271(9):703-7.
Etiology/Harm
Levine M ;
Walter S ; Lee H ; Haines T ; Holbrook A
; Moyer V. Users' guides to the medical
literature. IV. How to use an article
about harm. Evidence-Based Medicine
Working Group. JAMA 1994 May 25;
271(20):1615-9.
Prognosis
Laupacis A
; Wells G ; Richardson WS ; Tugwell P.
Users' guides to the medical literature.
V. How to use an article about
prognosis. Evidence-Based Medicine
Working Group. JAMA 1994 Jul 20;
272(3):234-7.

Useful links:
Oxford
Centre for Evidence Based Medicine
http://www.ebm-first.com
http://www.hsl.unc.edu/services/tutorials/srchdbs/splash.htm
http://www.bcdecker.com
http://www.mclibrary.duke.edu/training/ovid
http://www.cebm.net/ebm_is_isnt.asp
Duke
University Medical Center Library
Health
Sciences Library, UNC-Chapel Hill
I would like to join EBM group, what to
do?
Only
members of the MEFS will be able to
access
the EBM task team
facility. You will be redirected to the
application of the MEFS
membership form
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